Mineral Identification Key

The Mineral Identification Key

Copper, Michigan, Seaman Museum specimen

Table IIC-1: Streak not colored, Cleavage prominent, Hardness 2½ to 3: (Can not be scratched by a fingernail, can be scratched by a copper penny, streak white or one.) [Previous Table] [Next Table]

Cleavage Hardness Color Luster Name System Habit SG Notes

Perfect in one direction (basal) 2½ to 4 Lilac, Lavender, Greyish- to Greenish-white Pearly on cleavage surfaces LEPIDOLITE
(Mica Group)
K(Li,Al)₃(Si,Al)₄O₁₀(F,OH)₂ Monoclinic, pseudo-hexagonal Usually as aggregates of tiny flakes, also as "books" of larger sheets, rarely as diamond-shaped or distorted hexagonal shaped crystals, flakes or sheets 2.8 to
3.0 Elastic, harder than other common
micas – except for margarite (see below).

Perfect in one direction (basal) 3½ to 5 Deep to pale Lilac, Grey to White Pearly on cleavage surfaces MARGARITE
(Mica Group)
CaAl₂(Al₂Si₂)O₁₀(OH)₂ Monoclinic Usually as flaky aggregates or cross-grain "books" sandwiched in a matrix of chlorite-rich amphibolite schist 3.0 to 3.1 Bends little and then
breaks – "brittle mica." Hardest of the common micas.

Cleavage Hardness Color Luster Name System Habit SG Notes

Perfect in three directions (cubic) 2 Colorless to White (may be stained by impurities) Vitreous to sub-vitreous HALITE
(Common Salt, Rock Salt)
NaCl Isometric Usually as granular crystalline masses or small cubic crystals 2.17 Has a salty taste. Halite and sylvite can be hard to tell apart, but sylvite has a more bitter taste

Perfect in three directions (cubic) 2 Colorless to White (may be stained by impurities) Vitreous to sub-vitreous SYLVITE
(Potassium Salt)
KCl
Isometric Usually as granular crystalline masses or small cubic crystals 1.97 to 1.99 Has a salty taste. Sylvite and halite can be hard to tell apart, but sylvite has a more bitter taste

Distinct in one direction (prismatic), good in a second direction
(basal) and fair to poor in a third direction (rhombic overall) 2½ to 3 Colorless or White to Greyish-white or Greyish-brown Adamantine to sub-adamantine, may be vitreous to resinous on some surfaces ANGLESITE
PbSO₄ Orthorhombic Usually in crystalline masses, crystals usually small and tabular, rarely prismatic 6.2 to 6.4 Streak white;
Massive material may be difficult to distinguish from cerussite without testing for SO₄ vs. CO₃ (See cerussite below).

Cleavage Hardness Color Luster Name System Habit SG Notes

Perfect in three directions, corners 120^o or 60^o (rhombic) 3; but 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 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; 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. (there are over 800 crystals forms known for this species to date…) 2.71 White streak; 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.

Cleavage Hardness Color Luster Name System Habit SG Notes

Perfect in two directions (prismatic) and fair in a third 3 Colorless, White, or Grey (may be stained other colors) Vitreous to sub-vitreous KERNITE
Na₂B₄O₆(OH)₂^.3H₂O Monoclinic Usually in cleavable crystalline masses 1.95 Splintery cleavage fragments

Imperfect in one direction (basal), distinct in another direction
(rhombic), may not be 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.

Perfect in two directions, imperfect to good in a third 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 a pseudo-cubic cleavage, or in granular masses with no cleavage apparent, crystals rare and usually equant or thick tabular 2.9 to
2.98 Pseudo-cubic cleavage

Cleavage Hardness Color Luster Name System Habit SG Notes

Distinct in one direction (prismatic), good in a second direction
(basal) and fair to poor in a third direction (rhombic overall) 3 to 3½ Colorless to White or Greyish-white, may be tinted other colors Vitreous, pearly on basal cleavage
surfaces BARITE
BaSO₄ Orthorhombic Usually in clusters or aggregates of platy to tabular crystals 4.5 Distinguish from Celestine by SG or a flame test (lime green)

Distinct in one direction (prismatic), good in a second direction
(basal) and fair to poor in a third direction (rhombic overall) 3 to 3½ Colorless to White or Greyish-white, Blue, may be tinted other colors Vitreous, pearly on basal cleavage surfaces CELESTITE (Celestine)
SrSO₄ Orthorhombic Usually in clusters or aggregates of platy to tabular crystals 3.95 to 3.97 Distinguish from Barite by SG or a flame test (bright red)

Note: The above 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.
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Cleavage	Hardness	Color	Luster	Name	System	Habit	SG	Notes
Perfect in one direction (basal)	2½ to 4	Lilac, Lavender, Greyish- to Greenish-white	Pearly on cleavage surfaces	LEPIDOLITE (Mica Group) K(Li,Al)₃(Si,Al)₄O₁₀(F,OH)₂	Monoclinic, pseudo-hexagonal	Usually as aggregates of tiny flakes, also as "books" of larger sheets, rarely as diamond-shaped or distorted hexagonal shaped crystals, flakes or sheets	2.8 to 3.0	Elastic, harder than other common micas – except for margarite (see below).
Perfect in one direction (basal)	3½ to 5	Deep to pale Lilac, Grey to White	Pearly on cleavage surfaces	MARGARITE (Mica Group) CaAl₂(Al₂Si₂)O₁₀(OH)₂	Monoclinic	Usually as flaky aggregates or cross-grain "books" sandwiched in a matrix of chlorite-rich amphibolite schist	3.0 to 3.1	Bends little and then breaks – "brittle mica." Hardest of the common micas.
Cleavage	Hardness	Color	Luster	Name	System	Habit	SG	Notes
Perfect in three directions (cubic)	2	Colorless to White (may be stained by impurities)	Vitreous to sub-vitreous	HALITE (Common Salt, Rock Salt) NaCl	Isometric	Usually as granular crystalline masses or small cubic crystals	2.17	Has a salty taste. Halite and sylvite can be hard to tell apart, but sylvite has a more bitter taste
Perfect in three directions (cubic)	2	Colorless to White (may be stained by impurities)	Vitreous to sub-vitreous	SYLVITE (Potassium Salt) KCl	Isometric	Usually as granular crystalline masses or small cubic crystals	1.97 to 1.99	Has a salty taste. Sylvite and halite can be hard to tell apart, but sylvite has a more bitter taste
Distinct in one direction (prismatic), good in a second direction (basal) and fair to poor in a third direction (rhombic overall)	2½ to 3	Colorless or White to Greyish-white or Greyish-brown	Adamantine to sub-adamantine, may be vitreous to resinous on some surfaces	ANGLESITE PbSO₄	Orthorhombic	Usually in crystalline masses, crystals usually small and tabular, rarely prismatic	6.2 to 6.4	Streak white; Massive material may be difficult to distinguish from cerussite without testing for SO₄ vs. CO₃ (See cerussite below).
Cleavage	Hardness	Color	Luster	Name	System	Habit	SG	Notes
Perfect in three directions, corners 120^o or 60^o (rhombic)	3; but 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	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; 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. (there are over 800 crystals forms known for this species to date…)	2.71	White streak; 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.
Cleavage	Hardness	Color	Luster	Name	System	Habit	SG	Notes
Perfect in two directions (prismatic) and fair in a third	3	Colorless, White, or Grey (may be stained other colors)	Vitreous to sub-vitreous	KERNITE Na₂B₄O₆(OH)₂^.3H₂O	Monoclinic	Usually in cleavable crystalline masses	1.95	Splintery cleavage fragments
Imperfect in one direction (basal), distinct in another direction (rhombic), may not be 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.
Perfect in two directions, imperfect to good in a third	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 a pseudo-cubic cleavage, or in granular masses with no cleavage apparent, crystals rare and usually equant or thick tabular	2.9 to 2.98	Pseudo-cubic cleavage
Cleavage	Hardness	Color	Luster	Name	System	Habit	SG	Notes
Distinct in one direction (prismatic), good in a second direction (basal) and fair to poor in a third direction (rhombic overall)	3 to 3½	Colorless to White or Greyish-white, may be tinted other colors	Vitreous, pearly on basal cleavage surfaces	BARITE BaSO₄	Orthorhombic	Usually in clusters or aggregates of platy to tabular crystals	4.5	Distinguish from Celestine by SG or a flame test (lime green)
Distinct in one direction (prismatic), good in a second direction (basal) and fair to poor in a third direction (rhombic overall)	3 to 3½	Colorless to White or Greyish-white, Blue, may be tinted other colors	Vitreous, pearly on basal cleavage surfaces	CELESTITE (Celestine) SrSO₄	Orthorhombic	Usually in clusters or aggregates of platy to tabular crystals	3.95 to 3.97	Distinguish from Barite by SG or a flame test (bright red)