Many inorganic or organic compounds form crystals.
Granite, gabbro, and diorite are a few igneous rocks that forms crystals. Igneous rocks that form visible crystals are intrusive igneous rocks, rocks that form under the earth's surface.
a saturated solution will form crystals
Gneiss usually consists of visible crystals of aligned mineral assemblages.
Non-foliated metamorphic rock is composed of non-layered visible mineral crystals.
A supersaturated solution is most likely to form crystals as it cools.
The size of the crystals that do form are smaller/microscopic in that the time an temperature for crystals to grow is cut. The type of mineral that crystallizes is also effected,
A compound or open fracture, where the bone is visible sticking out of the skin
Obsidian is an example of a rapidly cooled rock, also known as volcanic glass.
it forms ingenous rock ...
Ummm... Really? Sugar crystals... Taste great!
Normally the crystals in extrusive igneous rock are small enough as to not be visible without magnification. The exception would be a porphyritic rock that has visible crystals dispersed in a fine-grained matrix. This type of rock represents a partial cooling of magma before expulsion by volcanism.
It forms a face-centered cubic crystals. Under pressure these change to hexagonal close packed (hcp) crystals.