Here's why:
* Crystals are naturally occurring solids with a highly ordered internal structure. This internal structure dictates the external shape of the crystal, resulting in geometric forms like cubes, pyramids, and prisms.
* Minerals are naturally occurring solid substances with a specific chemical composition and crystal structure.
* While some minerals can be quite hard, others, like talc, are very soft.
Therefore, a soft, geometric shape formed by a mineral is most likely a crystal of a soft mineral.
