The Mineral Identification Key Copper, Michigan, Seaman Museum specimen

Habit is the general appearance a mineral tends to have – whether it is found as blocky crystals, long slender ones, or aggregates of some type, etc.  If the crystals are glassy but cubic in shape you know they aren’t quartz.  If they are rounded like a soccer ball you know they aren’t tourmaline.  And so on…

Distinct crystals may be described as:



Blocky or Equant – Roughly box-like or ball-like, as in pyrite.

Rhodolite garnet, 8 cm across, Brazil
 


Tabular - Shaped like a pad of paper (thin tabular) or a deck of playing cards (thick tabular).

Barite 4cm across, Bolivia
 


Prismatic – Elongated with opposite faces parallel to one another, in which case they may be short and stout, or long and thin. Includes minerals such as quartz and tourmaline crystals

Tourmaline (elbaite) 9 cm tall, California
Tourmaline (elbaite) 9 cm tall, California
 


Bladed - Long thin crystals may be flattened like the blade of a knife.        Actinolite is often bladed.

Stibnite, 5cm across, Romania
 


Acicular – Needle-like.

Millerite, 1.5cm. long, Wisconsin
 


Filiform or Capillary – Like hair or thread.

Pyrite filament 0.2 mm long, New Mexico, Dan Behnke photograph

 

Groups of distinct crystals may be described as:



Druzy - Covering a surface in more-or-less outward pointing clusters of small crystals, such as druzy quartz crystals.

Quartz on chrysocolla, Mexico 2cm across
 


Divergent or Radiating - Growing outward from a point in sprays or starbursts, such as some hemimorphite exhibits.

Adamite 3.5 cm across,
 Mexico
 


Reticulated – Interconnected like a lattice or trellis, such as rutile.

Cerussite, Tsumeb, Namibia
 2 cm across
 


Dendritic or Arborescent - Slender divergent branch- or fern-like clusters, such as some native silver crystals.

Copper, Michigan, 4cm tall

 

Compact parallel or radiating groups of individual crystals may be described as:



Columnar – Stout parallel clusters with a column-like appearance, such as some forms of the serpentine minerals.

Quartz, 4cm tall, New Mexico
 


Fibrous – Aggregates of parallel or radiating slender fibers, such as chrysotile.

Silver 2cm across, Czech Republic
 


Stellate – Long thin crystals radiating outwards in all directions, like a starburst or in a circular pattern, such as astrophyllite.

Natrolite, 10 cm tall, Tasmania, Australia
Natrolite, 10 cm tall, Tasmania, Australia
 


Spherical or Globular – Compact clusters radiating outwards forming rounded, ball-like, shapes.

Azurite, 10cm across, Arizona
 The next three habits tend to grade into each other


Botryoidal – Globular or ball-like clusters – like a bunch of grapes.

Hematite,  2cm across, Wisconsin
 


Mammillary – Large rounded masses resembling human breasts.

Quartz variety chalcedony, 4cm across, Nebraska
 


Reniform – Radiating compact clusters of  crystals ending in rounded, kidney-like, surfaces, such as hematite often exhibits.

Hematite 6 cm across, Wisconsin
 

A mineral aggregate composed of scales or flakes may be described as:



Foliated – Looking like overlapping flakes or leaves and easily separable into individual leaves or flakes, usually at least somewhat "wavy" in appearance, such as the chlorite minerals.

Talc, 6 cm across, Michigan
Talc, 6 cm across, Michigan
 


Micaceous – Like foliated, but splits into very thin sheets, like the mica minerals.

Mica schist, Black Hills,
South Dakota, 10cm across
 


Lamellar – Flat, platy, grains thicker than flakes or leaves, but overlapping like foliated, such as molybdenite.

Molybdenite & 
ferrimolybdenite (yellow),
 Canada 3cm across.
 


Plumose – Feather-like sprays of fine scales, similar to dendritic but with a much finer structure, such as one form of native silver.

Manganese oxide dendrites, Grant Co. New Mexico 6 cm across
Manganese oxide dendrites, Grant Co. New Mexico 6 cm across

          A mineral composed of grains is simply said to be granular. Granular minerals may be composed of rounded or semi-rounded grains, or of angular grains.

 

A few other descriptive terms are:



Massive – No crystal structure visible, though the mineral may be crystalline.  Some massive minerals may also be granular.

Forsterite and magnetite,
 Arizona 3cm across
 


Banded – Showing different bands or layers of  color or texture, as in  some agates or some fluorite.

Goethite, 8 cm tall, Wisconsin
 


Concentric – In rounded masses showing layers around the mass in shells, working outward from the center, as in some agates.

Quartz var. Lake Superior agate, 5 cm across, Michigan
Quartz var. Lake Superior agate, 5 cm across, Michigan
 The next three habits tend to grade into each other, oolites and pisolites tend to be uncommon


Oolitic – Masses of small round spheres about the size of fish eggs (0.25-2.0mm).

Manganese oxide, 3cm across, Australia
 


Pisolitic - Roughly pea-size rounded masses.

Manganese oxide, 6cm across, Australia
 


Concretionary – Masses formed by mineral being deposited around a nucleus, may be spherical or rounded but may also be a wide variety of other shapes.


Top - outside of concretion,
 2cm across, Illinois; 
Bottom - interior of split 
concretion showing fern leaf fossil
 


Geode – A rock with a hollow, roughly spherical, interior with concentric bands of mineral (usually agate) on the wall and possibly crystals on the interior surface, pointing inwards.

Geode, with quartz and calcite crystals, 8cm across, Mexico
 

A wide variety of other terms are also used to describe mineral habits.  Usually they refer to loose associations with common objects or concepts and are readily apparent when the term is used in context with the form present in the mineral at hand.

[ Table of Contents ] [ Introduction ] [ Identification Kit ] [ Mineral Properties ] [ Environments & Associations ] [ In Conclusion ] [ The Mineral ID Key ]


[Previous] [Next]