* Calcite: This is the most common form of calcium carbonate. It's hexagonal and often found in clear, colorless, or white crystals. However, it can also be found in a variety of colors, including yellow, pink, and green.
* Aragonite: This form of calcium carbonate is orthorhombic, meaning it has three unequal axes at right angles to each other. It's often found in needle-like crystals or as a fibrous, branching mass.
* Vaterite: This form of calcium carbonate is rare and unstable. It has a hexagonal crystal structure, similar to calcite.
In addition to these three main forms, calcium carbonate can also occur as amorphous calcium carbonate which lacks a defined crystal structure. This form is often found in biological systems.
So, the answer to your question depends on the specific form you're interested in.
