The Mineral Identification Key |
Table IID-1: Nonmetallic Luster, Hardness Greater Than 3 but Less Than 5½, and Prominent Cleavage: (Can not be scratched by a copper penny, can be scratched by a knife, streak white or none.) [Previous Table] [Next Table]
Cleavage | Hardness | Color | Luster | Name | System | Habit | SG | Notes |
Imperfect in one direction (basal), may be distinct in another direction (rhombic) but usually not seen | 3 to 3½ | Colorless to White or Greyish-white, may be tinted other colors | Vitreous to sub-vitreous | WITHERITE (Aragonite Group) BaCO3 |
Orthorhombic, pseudo- hexagonal |
Usually as stout prismatic twinned crystals with a hexagonal cross section, often with pyramidal terminations on both ends, more rarely as globular to botryoidal clusters, coarse fibrous aggregates, and granular | 4.29 | Often hazed, will effervesce in cold acid. |
Distinct in one direction | 3½ to 4 | Colorless to White or Grey, may be tinted other colors | Vitreous to sub-vitreous or resinous | ARAGONITE (Aragonite Group) CaCO3 |
Orthorhombic | Usually in prismatic crystals, sometimes flattened, often acicular, usually twinned producing a pseudo-hexagonal cross section, may also be columnar, radiating or stellate aggregates, also stalactic | 2.95 | Often fluorescent, pale rose, yellow or bluish-white, effervesces in cold acids. Distinguished from calcite by its greater hardness, higher S.G. and different crystal forms and habits – though some crystals may mimic the forms found in calcite. |
Cleavage | Hardness | Color | Luster | Name | System | Habit | Sp. G | Notes |
Perfect cleavage in one direction | 3½ to 4 | Colorless to White, may be Yellow, Brown, and other colors | Vitreous, pearly on cleavage surfaces | STILBITE-(Ca) (Zeolite Group) (Ca0.5,Na,K)9[Al9Si27O72].28H2O |
Monoclinic | Usually as flattened tabular long prismatic crystals, often in sheaf-like groups ("bowties") | 2.12 to 2.22 | White streak; dissolves in cold acids. |
Perfect cleavage in one direction | 3½ to 4 | Colorless to White, may be Grey, Yellow, Pink, and other colors | Vitreous, pearly on cleavage surfaces | HEULANDITE-(Ca) (Zeolite Group) (Ca0.5,Na,K)9[Al9Si27O72].~24H2O |
Monoclinic | Commonly tabular to equant crystals, may be long-prismatic, typically coffin shaped | 2.10 to 2.29 | White streak; dissolves in cold acids. |
Perfect cleavage in one direction | 3½ to 4 | Colorless to White | Vitreous, pearly on cleavage surfaces | CLINOPTILOLTE-(Ca) (Zeolite Group) (Ca0.5,Na,K)6[Al6Si30O72].~20H2O |
Monoclinic | Usually as platy crystals, may be tabular or flattened long prismatic, commonly fine-grained, massive | 2.10 to 2.17 | White streak; dissolves in cold acids. |
Perfect cleavage in one direction | 4½ | Colorless to White, may be Pink or Brown | Vitreous to sub-vitreous | STELLERITE (Zeolite Group) Ca[Al2Si7O18].7H2O |
Orthorhombic | Usually in spheres of radiating elongated tabular crystals, often also as aggregates of scaly to platy and small tabular crystals | 2.13 | White streak; dissolves in cold acids. |
Perfect in one direction, may have a poor (pinacoidal) cleavage in another direction | 4½ to 5½ | Colorless to White, Pale-pink, Pale-yellow to Pale-brown | Vitreous, pearly on some cleavage surfaces | BREWSTERITE-Sr/ BREWSTERITE-Ba (Sr,Ba)2[Al4Si12O32].10H2O (Ba,Sr)2[Al4Si12O32].10H2O |
Monoclinic & Triclinic | Usually as small tabular crystals, may be blocky or prismatic as well | 2.32 to 2.45 | White streak; S.G. increases with Ba content; Brewsterite-Ba is the far more common of the two. |
Cleavage | Hardness | Color | Luster | Name | System | Habit | SG | Notes |
Perfect in one direction (prismatic) | 5 to 5½ | Colorless to White, Pale-pink, may be Grey or other colors | Usually vitreous to silky in finer acicular aggregates, but may be dull or even greasy | NATROLITE (Zeolite Group) Na2[Al2Si3O10].2H2O |
Orthorhombic | Usually as long slender needles in stellate clusters or radial aggregates, may also be in jackstraw clusters | 2.20 to 2.27 | White streak; partially decomposed by acid, producing a white gel. |
Poor in one direction, may not be seen | 5 to 5½ | Colorless to White, may be Yellow, Pink, or other colors | Vitreous | ANALCIME (Zeolite Group) Na[AlSi2O6].H2O |
Polymorphous (Iso., Tet., Orth., Mon., Tric., Trig.) | Usually in cubic or trapezohedral crystals or fine-grained masses, more rarely in other crystal forms | 2.22 to 2.63 | Dissolves in cold acids |
Perfect in one direction (may have a distinct cleavage in a second direction) | 4 to 4½ | Colorless to White or Grey, may be tinted other colors | Vitreous to sub-adamantine | COLEMANITE Ca2B6O11.5H2O |
Monoclinic | Usually druzy, massive granular, equant to short prismatic crystals | 2.42 | Decrepitates violently in a candle flame. |
Perfect in one direction (may have an imperfect cleavage in a second direction) | 4½ to 5 | Colorless to White or Grey, Pale-green, may also be other tints | Vitreous to sub-vitreous, pearly on cleavage surfaces | FLUORAPOPHYLLITE/ HYDROXYLAPOPHYLLITE KCa4Si8O20F.8H2O KCa4Si8O20(OH).8H2O |
Tetragonal | Crystals usually equant, blocky, may be stout tabular, more rarely prismatic, commonly striated | 2.33 to 2.37 | It is impossible to tell the two end members apart without subtle chemical tests. Information about which is found at any given locality is the best bet. Fluorapophyllite is probably the more common of the two. |
Cleavage | Hardness | Color | Luster | Name | System | Habit | SG | Notes |
Perfect in one direction (may have a good cleavage in another direction) | 4½ to 5 parallel to the length of the crystal, 7 to 7½ across the crystal | Blue most common, also Green, may be Grey, even Black, due to inclusions | Vitreous to subvitreous | KYANITE Al2SiO5 |
Triclinic | Most often as bladed long-prismatic crystals, usually poorly formed and rarely terminated, may be in parallel groupings or randomly oriented in the matrix | 3.56 to 3.76 | Only common mineral with significant hardness difference in two directions. |
Two directions: Perfect in one direction (prismatic), poor in another direction (prismatic) |
3½ to 4 | Colorless to White or Grey, may be tinted other colors | Vitreous to sub-vitreous, silky when fibrous | STRONTIANITE (Aragonite Group) SrCO3 |
Orthorhombic | Usually in granular or fibrous aggregates, may be columnar, crystals short prismatic to acicular, often pseudo-hexagonal in cross-section (Ca-rich) | 3.76 | Effervesces mildly in cold acids, or not at all. Distinguished from cerussite by its notably lower specific gravity, lighter feel. Also it is not as common as cerussite. |
Two directions: Perfect in one direction, imperfect in a second |
4½ | Bluish-grey to Greenish-Grey (triphylite), White to Greyish-white streak, Clove-brown to Yellowish-brown, Salmon (lithiophilite) | Vitreous to sub-vitreous, may be dull in granular massive material | TRIPHYLITE/ LITHIOPHILITE LiFePO4 LiMnPO4 |
Orthorhombic | Usually in cleavable crystalline masses, crystals rare and usually crude with uneven surfaces, stout prismatic | 3.56 (triphylite), 3.34 (lithiophilite) | |
Cleavage | Hardness | Color | Luster | Name | System | Habit | SG | Notes |
Two directions: Perfect in one direction (prismatic), poor in a second direction (cleavages rarely seen) | 4½ to 5 | Colorless to White, may be Pale-yellow, Pale-green, Sky-blue, Pale-brown | Vitreous, pearly on some cleavage surfaces | HEMIMORPHITE Zn4Si2O7(OH)2.H2O |
Orthorhombic | Usually in radiating clusters of acicular or somewhat flattened long prismatic crystals, may also be in thick botryoidal crusts of thick to almost fibrous radiating crystals | 3.4 to 3.5 | May resemble prehnite in its botryoidal form, but S.G. is higher |
Two directions: Perfect in both directions (pinacoidal) | 4½ to 5 | White, Pale-pink, Pale-tan, Pale-blue | Vitreous to silky in fibrous material | PECTOLITE (Wollastonite Group) NaCa2Si3O8(OH) |
Triclinic | Usually in acicular sprays or radial fibrous aggregates | 2.84 to 2.90 | Partly decomposed in acid forming a gel |
Two directions: Perfect in one direction (pinacoidal), good in a second (pinacoidal), may exhibit a poor to good third cleavage (rarely seen) | 4½ to 5 | White to Greyish-white, may also be Pale-green | Vitreous to somewhat pearly in fibrous material | WOLLASTONITE-1A (Wollastonite Group) CaSiO3 |
Triclinic | Usually in coarsely crystalline cleavage masses, more rarely fibrous | 2.86 to 3.09 | Most common of the wollastonite polymorphs. Found in contact metamorphism of siliceous limestones |
Cleavage | Hardness | Color | Luster | Name | System | Habit | SG | Notes |
Two directions: Perfect in two directions (both pinacoidal) | 4½ to 5 | Orange to Pinkish-orange to Rose | Vitreous, pearly on cleavage surfaces | SERANDITE (Wollastonite Group) Na(Mn,Ca)2Si3O8(OH) |
Triclinic | Usually as slightly flattened prismatic crystals in parallel to sub-parallel groups | 3.0 to 3.4 | Rare |
Two directions: Perfect in one direction, imperfect parting in a second direction (both prismatic) | 5 to 5½ | Yellowish-brown to Greenish-brown | Vitreous to sub-vitreous, may be somewhat resinous or oily | TITANITE ("SPHENE") CaTiSiO5 |
Monoclinic | Usually in crude blocky to stout prismatic crystals, wedge-shaped | 3.48 to 3.60 | Streak white to pale brown |
Two directions: Perfect in both directions at nearly 90o to one another (prismatic) | 5½ to 6½ | Pink to Rose-red, Brownish-red, usually coated with black manganese oxides | Vitreous to sub-vitreous, may be somewhat pearly on cleavage surfaces | RHODONITE (Mn,Fe,Mg,Ca)SiO3 |
Triclinic | Usually massive, granular, rarely as tabular crystals | 3.55 to 3.76 | |
Two directions: Perfect in two directions | 5½ to 6 | Dark Greenish-black to Black | Vitreous, splendant. | BABINGTONITE Ca2(Fe,Mn)FeSi5O14(OH) |
Triclinic | Usually as equant to stout prismatic to tabular crystals, often crude | 3.34 to 3.48 | Pale greenish to brownish grey streak |
Cleavage | Hardness | Color | Luster | Name | System | Habit | SG | Notes |
Two directions: Perfect in both directions (both pinacoidal) | 4 to 4½ | Colorless to White, may be Pink to Orange-red | Silky to vitreous | DACHIARDITE-Ca (Zeolite Group) |
Monoclinic | Usually fibrous to small bladed prismatic crystals in radiating aggregates or clusters | 2.14 to 2.21 | White streak; Rare. |
Two directions: Distinct in one direction, indistinct in another (both pinacoidal) | 4 to 4½ | Colorless to White, may be Pink to Red, Yellow | Vitreous | PHILLIPSITE-Ca (Zeolite Group) |
Monoclinic | Usually as small twinned, pseudo-orthorhombic, prismatic crystals | 2.2 | White streak; Forms a series with harmotome. |
Two directions: Good in one direction, fair in another (both pinacoidal), fair cleavage may not be seen | 4½ to 5 | Colorless to White or Greyish-white, may be tinted other colors | Vitreous | HARMOTOME (Zeolite Group) (Ba0.5,Ca0.5,K,Na)5[Al5Si11O32]·12H2O |
Monoclinic | Usually as blocky crystals, but may be twinned, pseudo-orthorhombic, prismatic crystals | 2.38 to 2.50 (increasing with Ba content) | Streak white; Forms a series with phillipsite |
Two directions: Perfect in one direction, poor in another, (pinacoidal), second may not be seen |
4½ to 5½ | Colorless to White, Pale-pink, Pale-yellow to Pale-brown | Vitreous, pearly on some cleavage surfaces | BREWSTERITE-Sr/ BREWSTERITE-Ba (Sr,Ba)2[Al4Si12O32].10H2O (Ba,Sr)2[Al4Si12O32].10H2O |
Monoclinic & Triclinic | Usually as small tabular crystals, may be blocky or prismatic as well | 2.32 to 2.45 (increasing with Ba content) | Brewsterite-Ba is the far more common of the two |
Cleavage | Hardness | Color | Luster | Name | System | Habit | SG | Notes |
Two directions: Perfect in both directions (both prismatic) | 5 | Colorless to White, may be Pink to Red, Yellowish or Green | Silky when fibrous, vitreous when acicular | MESOLITE (Zeolite Group) Na16Ca16[Al48Si72O240].64H2O |
Orthorhombic | Usually in fibrous radiating aggregates or long slender needles in sprays, stellate clusters, or jackstraw clusters, may also be fibrous tufts | 2.25 | White streak; |
Two directions: Perfect in both directions (both prismatic) |
5 to 5½ | Colorless to White, Pink to Red or Salmon, Green | Vitreous, silky in fibrous material | SCOLECITE (Zeolite Group) Ca[Al2Si3O10].3 H2O |
Monoclinic | Usually as thin flattened prismatic needles in stellate to radiating clusters, may also be in fibrous radiating aggregates | 2.24 to 2.31 | Rare. |
Two directions: Perfect in one direction (prismatic), good to distinct in a second direction (actually a parting, but distinct – prismatic) |
5 to 5½ | Colorless to White, Pale-pink to Pale-red, may be other colors | Vitreous, silky in more fibrous aggregates, more rarely greasy or dull | NATROLITE (Zeolite Group) Na2[Al2Si3O10].2H2O |
Orthorhombic | Usually as long slender needles or prismatic crystals (nearly square cross-section, pseudo-tetragonal) in radial aggregates or stellate or jackstraw clusters | 2.20 to 2.27 | White streak; partially decomposed by acid, producing a white gel. |
Two directions: Perfect in one direction, good in another (both pinacoidal), may not be seen |
5 to 5½ | Colorless to White, may be tinted other colors, white streak | Vitreous to pearly | THOMSONITE (Zeolite Group) Ca2Na[Al5Si5O20]. 6H2O |
Orthorhombic | Usually in granular masses, crystals vary from thin rectangular blades to blocky prismatic | 2.25 to 2.44 | Partially decomposed by acid, producing a white gel. |
Two directions at ~56o and ~124o : prismatic – Amphibole Group; Good to perfect in both directions | 5 to 6 | Grey to Lavender-blue or Pale-blue | Vitreous, silky in asbestiform varieties | GLAUCOPHANE/ FERROGLAUCOPHANE Na2(Mg3Al2)Si8O22(OH)2 Na2(Fe3Al2) Si8O22(OH)2 |
Monoclinic | Usually in lath-like crystal aggregates, striated along their length, and in fibrous ("asbestiform") aggregates ("crocidolite") | 3.02 to 3.42 (increasing with Fe content) | Pale-grey to bluish-grey streak; glaucophane usually light-grey to lavender-blue; ferroglaucophane usually darker. The glaucophanes and riebeckites are impossible to tell apart without subtle chemical or optical tests. |
Cleavage | Hardness | Color | Luster | Name | System | Habit | SG | Notes |
Two directions at ~56o and ~124o : prismatic – Amphibole Group; Good to perfect in both directions | 5 to 6 | Light-blue to Blue-black | Vitreous, silky in asbestiform varieties | MAGNESIORIEBECKITE/ RIEBECKITE Na2(Mg3Fe2)Si8O22(OH)2 Na2(Fe3Fe2)Si8O22(OH)2 |
Monoclinic | Usually in lath-like crystal aggregates, striated along their length, and in fibrous ("asbestiform") aggregates ("crocidolite") | 3.02 to 3.42 (increasing with Fe content) | Pale-grey to bluish-grey streak; magnesioriebeckite usually lighter blue, riebeckite usually darker; glaucophanes and riebeckites are impossible to tell apart without subtle chemical or optical tests. |
Two directions at ~56o and ~124o : prismatic – Amphibole Group; Perfect in both directions | 5 to 6 | White to Light-Green to Dark-green | Vitreous, silky in asbestiform varieties | TREMOLITE/ ACTINOLITE Ca2Mg5Si8O22(OH)2 Ca2(Fe,Mg)5Si8O22(OH)2 |
Monoclinic | Usually in bladed crystal aggregates, may also be somewhat acicular, tremolite may be asbestiform ("byssolite") or in fibrous mats ("mountain leather", "mountain cork"). The massive fibrous aggregate form of either is known as the variety nephrite, and is one of the materials called 'Jade.' | 2.89 to 3.44 (increasing with Fe content) | Tremolite usually white to greyish-white or pale greenish-white, actinolite medium- to dark-green. |
Two directions at ~56o and ~124o : prismatic – Amphibole Group; Good to perfect in both directions | 5 to 6 | Brown to Greenish-brown to Green or Greyish-green | Vitreous, silky in fibrous varieties | CUMMINGTONITE/ GRÜNERITE Mg7Si8O22(OH)2 Fe7Si8O22(OH)2 |
Monoclinic | Usually in bladed crystal aggregates or asbestiform, may be acicular | 3.1 to 3.6 (increasing with Fe content) | Cummingtonite usually green to grey-green, grünerite brown to greenish-brown. |
Cleavage | Habit | Color | Luster | Name | System | Habit | SG | Notes |
Two directions at ~56o and ~124o : prismatic – Amphibole Group; Perfect in one direction, imperfect in the second | 5½ to 6 | White to Grey or Pale-green to Clove-brown or Dark-brown | Vitreous, silky in asbestiform varieties | ANTHOPHYLLITE/ FERROANTHOPHYLLITE Mg7Si8O22(OH)2 Fe7Si8O22(OH)2 |
Orthorhombic | Usually columnar aggregates, may be radiating, or asbestiform | 3.18 to 3.57 (increasing with Fe content) | Anthophyllite usually lighter colors, ferroanthophyllite darker. |
Two directions at ~56o and ~124o : prismatic – Amphibole Group; Perfect in one direction, imperfect in the other | 5½ to 6 | Pale Greenish-grey to Greenish-brown and Brown | Vitreous, silky when fibrous | GEDRITE/ FERROGEDRITE Mg5Al2[Si6Al2O22](OH)2 Fe5Al2[Si6Al2O22] (OH)2 |
Orthorhombic | Usually in lamellar to fibrous aggregates | 3.18 to 3.57 (increasing with Fe content) | Gedrite usually paler shades, ferrogedrite darker. |
Two directions at ~56o and ~124o : prismatic – Amphibole Group; Perfect in both directions | 5 to 6 | Black to Greenish-black or Dark-green | Vitreous | MAGNESIOHORNBLENDE/ FERROHORNBLENDE Ca2[Mg4(Al,Fe)]Si7AlO22(OH)2 Ca2[Fe4(Al,Fe)]Si7AlO22(OH)2 |
Monoclinic | Usually in coarsely crystalline cleavable masses, also in prismatic to acicular crystal aggregates with the crystals often displaying a crudely pseudo-hexagonal cross section, otherwise rectangular to nearly square, not asbestiform | 3.02 to 3.45 (increasing with Fe content) | May give grey-green streak; magnesiohornblende usually paler than ferrohornblende |
Cleavage | Hardness | Color | Luster | Name | System | Habit | SG | Notes |
Two directions at ~56o and ~124o : prismatic – Amphibole Group; Perfect in both directions | 5 to 6 | Pale-green to Dark-green, Greyish-brown to Brown, Yellow-brown to Reddish-brown or Rose-red | Vitreous, silky in asbestiform varieties | RICHTERITE/ FERRORICHTERITE Na(Ca,Na)Mg5Si8O22(OH)2 Na(Ca,Na)Fe5Si8O22(OH)2 |
Monoclinic | Usually in cleavable prismatic crystal aggregates or stout flattened prismatic crystals, also asbestiform | 2.97 to 3.45 (increasing with Fe content) | Color darkens with increasing Fe content (ie: ferrorichterite). |
Two directions at nearly 90o: prismatic – Pyroxene Group; Good to perfect in both directions | 5 to 6 | Pale to Medium-green, Pale-yellow to Light Yellowish-brown, Pale-bronze ("bronzite") | Vitreous to sub-vitreous, may be sub-metallic in the "bronzite" and "hypersthene" varieties | ENSTATITE/ CLINOENSTATITE Mg2Si2O6 |
Orthorhombic & Monoclinic | Usually granular in rocks, rarely as short-prismatic crystals | 3.21 to 3.60 | Enstatite-ferrosilite and clinoenstatite-clinoferrosilite form solid solution series. They are very difficult to tell apart. "Bronzite" and "hypersthene" are varietal names for intermediate members of the series. |
Cleavage | Hardness | Color | Luster | Name | System | Habit | SG | Notes |
Two directions at nearly 90o: prismatic – Pyroxene Group; Good in both directions | 5 to 6 | Greenish-brown or Brown to nearly Black | Vitreous to sub-vitreous, may be dull, may be pearly to sub-metallic on cleavage surfaces | FERROSILITE/ CLINOFERROSILITE (Fe,Mg)2Si2O6 |
Orthorhombic & Monoclinic | Usually granular in rocks, prismatic crystals rare | 3.6 to 4.0 | Streak pale grey to pale brown; Enstatite-ferrosilite and clinoenstatite - clinoferrosilite form solid solution series. They are very difficult to tell apart. "Bronzite" and "hypersthene" are varietal names for intermediate members of the series. |
Two directions at nearly 90o: prismatic – Pyroxene Group; Good to perfect in both directions | 5½ to 6 | Pale- to Dark-green, may be White or Greenish-white to Greyish-white | Vitreous to sub-vitreous, may be dull | DIOPSIDE CaMgSi2O6 |
Monoclinic | Usually as equant to stout prismatic crystals, slender prismatic less common, more rarely tabular, also massive and granular | 3.22 to 3.45 | White to pale-green streak; may exhibit chatoyancy and 4-ray asterism when cut and polished with the correct orientation. Diopside and hedenbergite form a solid solution series. They can be impossible to distinguish visually. S.G. usually tells them apart, though when of intermediate composition this may not do the trick. |
Two directions at nearly 90o: prismatic – Pyroxene Group; Good in both directions | 5½ to 6 | Pale- to Dark-green, Brownish-green to Brownish- or Greenish-black | Vitreous to sub-vitreous, may be dull | HEDENBERGITE CaFe Si2O6 |
Monoclinic | Usually as massive, granular, and as fracture fillings in rock, crystals equant to stout prismatic, slender prismatic less common, more rarely tabular | 3.45 to 3.56 | Pale green to tan streak; may exhibit chatoyancy and 4-ray asterism when cut and polished with the correct orientation. Diopside and hedenbergite form a solid solution series. They can be impossible to distinguish visually. S.G. usually tells them apart, though when of intermediate composition this may not do the trick. |
Cleavage | Hardness | Color | Luster | Name | System | Habit | SG | Notes |
Two directions at nearly 90o: prismatic – Pyroxene Group; Good in both directions | 5½ to 6 | Greenish-black to Black, Light- to Dark-brown | Vitreous to sub-vitreous, may be dull | AUGITE (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6 |
Monoclinic | Usually granular in rocks, also as somewhat flattened short-prismatic crystals | 3.19 to 3.56 | Pale brown to greenish grey streak |
Two directions at nearly 90o: prismatic – Pyroxene Group; Good to perfect in both directions | 5½ to 6 | Dark-green or Reddish-brown to Black | Vitreous to sub-vitreous, may be dull | AEGIRINE (ACMITE) NaFeSi2O6 |
Monoclinic | Usually as slender prismatic or acicular crystals, either in clusters in cavities or as acicular aggregates in matrix | 3.50 to 3.60 | Pale tan to yellow green to pale green streak |
Cleavage | Hardness | Color | Luster | Name | System | Habit | SG | Notes |
Three directions: rhombohedral – Trigonal Carbonates: Perfect in all three directions | 3, may be 2 across the top surface of prismatic crystals with a flat termination | Usually Clear or White to Tan or Grey, but may be tinted many colors | Vitreous to sub-vitreous luster, may be waxy or dull on weathered crystals, pearly on cleavage surfaces | CALCITE CaCO3 |
Trigonal | May be in cleavable masses producing rhombs, granular masses (limestone and marble), scalenohedral ("dogtooth") crystals, rhombohedral crystals, flattened rhombohedral ("nailhead") crystals, or a wide variety of related shapes (there are over 800 crystals forms known for this species to date…) | 2.71 | Clear rhombs show a doubled image of print viewed through them, , effervesces in cold, dilute acid – even in vinegar or Coke to a small degree. The many varied habits of calcite crystals make this one of the species that can be tough to identify by crystal form alone. Few people, if any, are familiar with all the forms it takes. |
Three directions: rhombohedral – Trigonal Carbonates: Perfect in all three directions | 3½ to 4½ | White to Grey, may be tinted Yellowish to Brownish | Vitreous to sub-vitreous, may be pearly on cleavage surfaces | MAGNESITE (Calcite Group) MgCO3 |
Trigonal | Usually massive, granular, crystals may be rhombohedral or prismatic but are rare | 3.0 | White streak; only slightly soluble in cold acids. No where near as common as calcite or dolomite. |
Three directions: rhombohedral – Trigonal Carbonates: Perfect in all three directions | 3½ to 4 | White to Tan or Pink, Grey, Greenish, tends towards Brown with increasing Fe, Red with Mn | Usually vitreous to sub-vitreous, but may be pearly | DOLOMITE CaMg(CO3)2 |
Trigonal | Usually as massive, granular, or in curved rhombohedral crystal clusters "fingernail" shape, druzes may have a characteristic "saddleback" arrangement | 2.85 | Streak same color as sample, but pale; powder effervesces in cold acid, though not as vigorously as calcite, may be fluorescent. The Dolomite Group minerals are best told apart – and from calcite – by their S.G. when color and habit coincides. |
Cleavage | Hardness | Color | Luster | Name | System | Habit | SG | Notes |
Three directions: rhombohedral – Trigonal Carbonates: Perfect in all three directions | 3½ to 4 | White to Tan or Brown | Usually vitreous to subvitreous, but may be pearly | ANKERITE (Dolomite Group) Ca(Fe,Mg,Mn)(CO3)2 |
Trigonal | Usually massive, granular, or as rhombohedral crystals (similar to dolomite) | 2.87 | White streak; powder effervesces in cold acids, though not as vigorously as calcite. Not as common as either calcite or dolomite. The Dolomite Group minerals are best told apart – and from calcite – by their S.G. when color and habit coincides. |
Three directions: rhombohedral – Trigonal Carbonates: Perfect in all three directions | 3½ to 4 | White to Pale-rose | Vitreous to sub-vitreous, but may be pearly | KUTNOHORITE (Dolomite Group) Ca(Mn,Mg,Fe) (CO3)2 |
Trigonal | Usually massive crystalline cleavable into rhombs, more rarely as rhombohedral crystals | 3.12 | White streak; powder effervesces in cold acids, though not as vigorously as calcite. Rare. The Dolomite Group minerals are best told apart – and from calcite – by their S.G. when color and habit coincides. |
Three directions: rhombohedral – Trigonal Carbonates: Perfect in all three directions | 3½ to 4 | Pink to Red (purer), in various shades, also more rarely Yellow-grey or Tan to Brown | Vitreous to sub-vitreous, may be pearly on cleavage surfaces | RHODOCHROSITE (Calcite Group) MnCO3 |
Trigonal | Usually in coarsely crystalline cleavable masses, crystals rhombohedral, may also be botryoidal and globular with concentric banding, and stalactic | 3.5 to 3.7(pure) | White streak; only slightly soluble in cold acids. Uncommon. |
Cleavage | Hardness | Color | Luster | Name | System | Habit | SG | Notes |
Three directions: rhombohedral – Trigonal Carbonates: Perfect in all three directions | 4 to 4½ | Greyish-white to Dark-grey, Greenish- or Brownish-white, may be Green to Apple-green, Blue to Blue-green, Yellow, Pink or Brown | Vitreous to sub-vitreous, may look somewhat porcelain-like | SMITHSONITE (Calcite Group) ZnCO3 |
Trigonal | Usually in botryoidal, reniform, and stalactic masses, rhombohedral crystals rare and usually crude with somewhat curved and rough surfaces, druzy | 4.2 (pure) | White streak; soluble in cold acids, though not with the vigorous effervescence of calcite. |
Three directions: rhombohedral – Trigonal Carbonates: Perfect in all three directions | 3½ to 4 | Dark-brown to Tan to Cream, may be Blackish-brown due to weathering | Vitreous to sub-vitreous, may be oily to resinous on weathered, oxidized surfaces | SIDERITE (Calcite Group) FeCO3 |
Trigonal | Usually in cleavable coarsely crystalline masses, though not cleavable into rhombs, crystals rhombohedral, more rarely tabular, very rarely prismatic | 3.8 to 4.0 | White streak; somewhat soluble in cold acids, but with little or no effervescence |
Three directions: Perfect to distinct in all three directions, rhombohedral | 3 to 5 | Colorless to White, may be tinted various colors | Vitreous to sub-vitreous | CHABAZITE-Ca (Zeolite Group) (Ca0.5,K,Na)4[Al4Si8O22].12H2O |
Triclinic, pseudo-trigonal | Usually as distorted cubes or pseudo-rhombohedral crystals (actually composed of six triclinic twins), rarely prismatic or tabular, then somewhat lens- or bean-shaped ("phacolitic") | 1.97 to 2.20 | Streak white; partially dissolved in cold acids producing a gel, may be fluorescent. |
Cleavage | Hardness | Color | Luster | Name | System | Habit | SG | Notes |
Three directions: Perfect to distinct in all three directions, rhombohedral | 4 to 4½ | Colorless to White, may be tinted various colors | Vitreous to subvitreous | LEVYNE-Ca (Zeolite Group) (Ca0.5,Na,K)6[Al6Si12O36].~17H2O |
Trigonal | Usually as small to tiny platy hexagonal crystals | 2.09 to 2.16 | Streak white; Rare. |
Three directions: Perfect in two directions, imperfect in a third, one prismatic | 3 to 4 | White, may be tinted other colors | Vitreous, pearly on cleavage surface, chalky when dehydrated | LAUMONTITE (Zeolite Group) Ca4[Al8Si16O48].18H2O |
Monoclinic | Usually as simple prismatic crystals with a square cross section, more rarely as equant crystals | 2.20 to 2.41 | White streak; crystals may have chalky white coatings due to dehydration, may be fluorescent. Rare. |
Three directions: One direction perfect, one imperfect, both pinacoidal, one good, basal | 3 to 3½ | Colorless to White, usually tinted other colors | Vitreous to sub-vitreous, may be pearly on cleavage surfaces | ANHYDRITE CaSO4 |
Orthorhombic | Usually in coarsely crystalline masses showing pseudo-cubic cleavage, or granular or fibrous, crystals uncommon and usually equant or thick tabular | 2.98 | White streak; dissolves in cold acids without effervescence |
Cleavage | Hardness | Color | Luster | Name | System | Habit | SG | Notes |
Three directions: Perfect in two directions, basal and pinacoidal, imperfect in a third, prismatic (rhombic overall) | 3 to 3½ | Colorless to White or Greyish-white, may be tinted other colors, streak white | Vitreous, pearly on basal cleavage surfaces | BARITE BaSO4 |
Orthorhombic | Usually in clusters or aggregates of platy to tabular crystals | 4.5 | Heavy for its size. The three members of the Barite Group are most easily told apart by their S.G.s. Anglesite is noticeably heavier than the other two, barite may feel heavier than celestite. |
Three directions: Perfect in one direction, basal, good in a second pinacoidal and fair to poor in a third, prismatic (rhombic overall) | 3 to 3½ | White to Greyish-white, Blue, may be tinted other colors, streak white | Vitreous, pearly on basal cleavage surfaces, | CELESTITE (Celestine) (Barite Group) SrSO4 |
Orthorhombic | Usually in clusters or aggregates of platy to tabular crystals | 3.95 to 3.97 | Somewhat heavy for its size. The three members of the Barite Group are most easily told apart by their S.G.s. Anglesite is noticeably heavier than the other two, barite may feel heavier than celestite. |
Three directions: One distinct (prismatic), second direction good (basal), and fair to poor in a third, (pinacoidal); rhombic overall – may be difficult to see all three | 2½ to 3 | Colorless to White or Greyish-white to Greyish-brown | Adamantine to sub-adamantine, may be vitreous to resinous on some surfaces | ANGLESITE (Barite Group) PbSO4 |
Orthorhombic | Usually in crystalline masses, crystals usually small and tabular, rarely prismatic | 6.2 to 6.4 | Streak white; very heavy. Massive material may be difficult to distinguish from cerussite if cleavages can't be seen. The three members of the Barite Group are most easily told apart by their S.G.s. Anglesite is noticeably heavier than the other two, barite may feel heavier than celestite. |
Cleavage | Hardness | Color | Luster | Name | System | Habit | SG | Notes |
Three directions: One direction perfect, one imperfect, both pinacoidal, one good, basal | 3 to 3½ | Colorless to White or Greyish-white, may be tinted other colors | Vitreous and/or pearly. | ANHYDRITE CaSO4 |
Orthorhombic | Usually in coarsely crystalline masses exhibiting pseudo-cubic cleavage, or in granular masses with no apparent cleavage, crystals rare and usually equant or thick tabular | 2.9 to 2.98 | White streak; |
Four directions: Perfect in all four directions, octahedral | 4 | Colorless, Green, Purple, Blue, Yellow, Pink | Vitreous | FLUORITE CaF2 |
Isometric | Usually in cubic crystals or coarsely crystalline masses exhibiting octahedral cleavage, crystals may also be octahedral | 3.18 | Streak white; often fluorescent. The term fluorescent is derived from this mineral's name. |
Four directions: Imperfect to distinct in two directions, prismatic; good in two directions, pinacoidal | 5 to 6 | White to Grey, Yellowish, Brownish, Orange, Purple | Vitreous to subvitreous, may be dull also | MARIALITE/ MEIONITE (Scapolite series) 3NaAlSi3O8.NaCl 3CaAl2Si2O8.CaCO3 |
Tetragonal | Usually massive, either columnar or fibrous, with columnar masses exhibiting cleavage surfaces, also as short to medium prismatic crystals with bipyramidal terminations, usually somewhat crude | 2.55 to 2.72 | May fluoresce yellow. It is almost impossible to tell the end members of this complex series apart without subtle chemical or optical tests. Intermediate member, wernerite, is probably the most common chemical form found – though it is not recognized as a species in spite of evidence that it should be. It is probably best to label samples of these materials simply as scapolite, unless specific locality information dictates otherwise |
Cleavage | Hardness | Color | Luster | Name | System | Habit | SG | Notes |
Six directions: Perfect in all six directions, dodecahedral, but difficult to produce in some of them | 3½ to 4 | Brown to Black, Yellow-brown to Greenish-yellow-brown, may also be Red ("Ruby Jack") in small crystals | Resinous, but may be oily or sub-metallic on cleavage surfaces and adamantine in small crystals | SPHALERITE (Zn,Fe)S |
Isometric | Usually in coarsely crystalline cleavable masses exhibiting seemingly chaotic cleavage surfaces, and as small tetrahedral (wedge-shaped) or dodecahedral (soccer ball-shaped) crystals, larger crystals tend to be somewhat crude and rough surfaced aggregates | 3.9 to 4.1 | Brown to yellow streak |
Six directions: Poor to distinct in all six directions, dodecahedral, may not be seen | 5½ to 6 | Medium-blue to Violet-blue, Greyish-white to White, more rarely Greenish- or Yellowish-white | Vitreous to subvitreous, may be somewhat dull in massive material | SODALITE Na8Al6Si6O24Cl2 |
Isometric | Usually as granular masses or grains in matrix, sometimes crudely cleavable, crystals rare, usually dodecahedral to cubo-dodecahedral, rarely octahedral | 2.14 to 2.30 | White to very pale blue streak; usually associated with nepheline – never with quartz. |
Six directions: Poor to distinct in all six directions, dodecahedral, may not be seen | 5 to 5½ | Deep-blue to Medium-blue or Violet-blue, may be Greenish-blue, Colorless | Dull to vitreous | LAZURITE (Sodalite Group) |
Isometric, Triclinic, and Monoclinic polytypes | Usually as compact massive material or grains, crystals rare, usually well-formed dodecahedral to cubo-dodecahedral | 2.38 to 2.45 | Bright blue streak; usually found with pyrite. |
Notes:
Single and double cleavage direction Zeolites can be difficult to tell apart. Hardness may help to distinguish the harder and softer species from one another, and crystal habit and form may help to tell some species apart. In general, habits and forms taken with hardnesses are the best indicators.Amphiboles are a large and difficult group to tell apart. The best bet is location-specific knowledge.
Pyroxenes can be difficult to distinguish from one another. Locality information is usually the best bet for determining what you have.
[ Table of Contents ] [ Introduction ] [ Identification Kit ] [ Mineral Properties ] [ Environments & Associations ] [ In Conclusion ] [ The Mineral ID Key ]
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