Crystal Habit
The term "crystal habit" is used to identify the shape, size and appearance of a crystal's unique growth characteristics, or "Crystal Forms". Crystal habits are useful in communicating what specimens of a particular mineral would, or should look like. There are approximately 36 standardized terms to describe the variations, or habits of crystal growth. A particular mineral may exhibit several different habits, all of which are influenced by the following factors:
- 1. Crystal Twinning ( two individual crystals share some of the same crystal lattice points)
- 2. Growth Conditions (heat, pressure, and space)
- 3. Trace Impurities (present during crystal formation)
When one mineral replaces another while preserving the original mineral's growth habit it is called a "pseudomorphous replacement. Most gemstone crystals are not found as perfectly formed single crystals but are found as aggregates of several crystals grown together in one mass.
Gemstones and their Crystal Habits
| Crystal Habit: |
Habit Description: |
Mineral: |
| Acicular |
Needle-like, slender and/or tapered |
Rutile (Quartz) |
| Anhedral |
Poorly formed and distorted |
Olivine |
| Banded |
narrow bands of differing colors |
Onyx |
| Bladed |
Slender, flattened and blade-like |
Tanzanite |
| Columnar |
Long, slender prisms and parallel growth |
Calcite |
| Dendritic |
Tree-like multi-directional branching from central point |
Opal |
| Dodecahedral |
12-sided Dodecahedron |
Garnet |
| Drusy (Encrustation) |
Aggregate of minute crystals coating a surface |
Drusy (Quartz) |
| Enantiomorphic |
Mirror-image (left/right) habit and optical characteristics |
Citrine, Amethyst |
| Equant (Stubby) |
Squashed, pinnacoids dominant over prisms |
Zircon |
| Euhedral |
Well-formed and Undistorted |
Spinel |
| Foliated |
Easily separated into plates |
Mica |
| Geode |
Rock cavities with internal crystals & encrustation |
Amethyst, Quartz |
| Granular Mass |
Anhedral crystals in lumpy mass with no crystal form |
Peridot |
| Mamillary |
Intersecting large rounded contours |
Malachite |
| Massive |
Shapeless with no distinct external crystal shape |
Lapis Lazuli |
| Octahedral |
Eight-sided octahedron - two pyramids, base to base |
Diamond |
| Pincoid |
Terminated by multiple pyramidal faces |
Emerald, Beryl |
| Prismatic |
Elongate and Prism-Like, all faces are parallel to c-axis |
Tourmaline, Topaz |
| Pseudomorphous |
Occurring in the shape of another mineral |
Tiger's Eye |
| Striated |
Surface growth lines parallel or perpendicular to c-axis |
Alexandrite |
| Tabular (Lamellar) |
Flat, tablet-shaped, prominent pinnacoid |
Ruby |
1. Acicular Crystal Habit
Three variations of Acicular Rutilated Quartz
2. Bladed Crystal Habit
Bladed Tanzanite (center) and Kyanite (right)
3. Columnar Crystal Habit
Columnar Quartz (left), Smoky Quartz (center), and Basalt Rock (Yellowstone, Wyoming) Formations (right)
4. Dendritic Crystal Habit
Dendritic Agate (left), Opal (center), and Agate (right)
5. Dodecahedral Crystal Habit
Dodecahedral Garnet (center), Diamond Rough (right)
6. Drusy Crystal Habit
Three variations of Druzy Quartz
7. Enantiomorphic Crystal Habit
Enantiomorphic ("Japan Law" or "Left-Right" Twins) Quartz (center), Amethyst (right)
8. Equant Crystal Habit
Equant Zircon Roughs (center, and right)
9. Euhedral Crystal Habit
Euhedral (Octahedral) Red Spinel (center, and right)
10. Geode Crystal Habit
Uncut Geode (left), Amethyst Geode (center), and Quartz Geode (right)
11. Granular Mass Habit
Granular Mass Peridot (center), and Peridotite Encrustation (right)
12. Mamillary Crystal Habit
Mamillary Malachite (center), and Chalcedony (right)
13. Octahedral Crystal Habit
Octahedral White Spinel (center), Diamond Rough (right)
14. Pincoid Crystal Habit
Pincoid (Prismatic) Aquamarine (center), Emerald (right)
15. Striated Crystal Habit
Striated (Prismatic) Tourmaline (center), Striated Sapphire (right)
16. Tabular Crystal Habit
Tabular Calcite (center), Ruby (right)
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Bibliography & Suggestions for Further Study on Crystal Habits
1. Indiana University, Molecular Structure Center - Cubic System  . www.iumsc.indiana.edu
2. Tulane University, External Symmetry of Crystals . www.tulane.edu
3. University of Wisconsin, The 48 Special Crystal Forms . www.uwgb.edu
4. Web Mineral, Minerology Database - Crystallography and Minerals by Crystal Form . webmineral.com
5. Rockhounds, Introduction to Crystallography . www.rockhounds.com
6. Judith Crowe, The Jeweler's Directory of Gemstones . DK Publishing.
7. Walter Schumann, Gemstones of the World . NAG Press; 2Rev Ed edition
8. Renee Newman, Gemstone Buying Guide . International Jewelry Publications; 2nd edition
9. Antoinette L . Matlins, Antonio C. Bonanno, Gem Identification Made Easy . Gemstone Press; 3rd edition
10. Paul R. Shaffer, Herbert S. Zim, Raymond Perlman, Rocks, Gems and Minerals . Martin's Press
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