Rock IdentifierCrystal Systems & Habits
Key takeaways
- There are seven crystal systems, set by the internal atomic symmetry.
- Habit is the shape a crystal actually grows in a given setting.
- Terms like druzy, botryoidal, and geode describe common habits collectors love.
System vs habit
Two related ideas cause confusion. A crystal system is the underlying symmetry of the atomic lattice — fixed for a given mineral. Habit is the outward shape an individual crystal grows, which depends on space, temperature, and chemistry. Halite always belongs to the cubic system, but its habit can range from perfect cubes to hopper-shaped skeletons.
The seven systems
Mineralogists sort crystals into seven systems by their axes and angles:
- Cubic (isometric) — pyrite, halite, garnet, diamond
- Tetragonal — zircon, rutile
- Hexagonal — quartz, beryl, apatite
- Trigonal — calcite, tourmaline, corundum
- Orthorhombic — topaz, olivine, barite
- Monoclinic — gypsum, orthoclase, mica
- Triclinic — plagioclase feldspar, turquoise
Common habits to recognize
Habit is often what you notice first. Prismatic crystals are elongated columns (quartz points); tabular ones are flat plates; acicular ones are needle-like. Druzy is a carpet of tiny sparkling crystals lining a surface. Botryoidal looks like a cluster of grapes or bubbles (malachite, hematite). Massive means no visible crystal shape at all — just a solid lump.
Geodes, nodules, and matrix
A geode is a hollow rock lined inside with inward-pointing crystals or banded agate — a cavity that became a crystal garden. A solid version with no hollow is a nodule. The host rock a crystal sits on is called the matrix, and a well-formed crystal still attached to attractive matrix is often more prized than a loose one.
