Important characteristics to observe in rocks include:

A) types of minerals present
B) sizes and shapes of crystals
C) presence or absence of layers
D) all of the above

Crystals

Solid materials whose constituents, such as atoms, molecules, or ions, are arranged in a highly ordered microscopic structure.

Minerals

Naturally occurring inorganic substances with a definite chemical composition and crystalline structure, forming the building blocks of rocks.