Crystal Habit (Shapes)
The six crystal systems of Crystallography describe the patterns of the molecules of crystals. Crystals can also be described by their external shape or “habit”. Terms for crystal shapes include acicular (needlelike), bladed (flat with sharp edges), equant (roughly equal length sides), filiform (hairlike), prismatic (elongated), pyramidal (shaped like single or double pyramids) and tabular (flat with flat, perpendicular edges).
The way minerals grow is greatly affected by the environment and temperature in which they form. Minerals deposited in sedimentary environments are usually earthy (masses of densley packed powder), stalactitic (shaped like stalactites), oolitic or (masses of spherical grains) and sometimes massive (solid and chunky). Igneous minerals are usually crystalline (varioius crystal shapes), massive (solid and chunky) and sometimes cleavable (crystalline masses that can be cleaved).