Cleavage is the way that a mineral breaks along well defined planes of weakness. The planes are between layers of atoms or other places where the atomic bonding is the weakest. Most cleavage surfaces are not always perfectly smooth like crystal faces, although they are very consistent and reflect light evenly. Cleavage is described as perfect, distinct, indistinct, or none.

The color of a mineral is a useful identification feature. Although it helps to identify minerals, color identification can trick you. Many minerals, like quartz, occur in a lot of different colors, and many minerals are boring white or even colorless.

If you hit a mineral with a geological hammer, it breaks, leaving the surfaces rough and uneven. This is called fracture. Cleavage surfaces are usually flat and exactly the same. Fractures are not the same each time. Common fracture terms are uneven, shell-like, jagged, and splintery.

Hardness is also a way to identify a mineral or rock. Hardness is the measurement of how resistant the mineral is to being scratched. On the Mohs' scale, the softest mineral is talc to the hardest mineral, diamond. The chart was created by Friedrich Mohs. Minerals with higher numbers will scratch those with lower numbers. You can also scratch minerals with household objects. For example: any mineral scratched by a coin has a hardness less than 3 1/2.

Comparing the weight of a mineral with the weight of an equal volume of water gives a mineral's specific gravity. This is shown in numbers. An S.G. of 2 1/2 shows a mineral weighs 2 1/2 times as much as water.

Transparency refers to the way light passes through a mineral sample. It varies, depending on the way the mineral atoms are bonded together. Mineral samples that you can see through are transparent. If you can not see through it, the mineral sample is translucent. When no light can pass through the mineral, even when it is cut very thin, it is opaque.

The color of a mineral's powder is called streak. You can see the streak of a mineral by rubbing the rock across the surface of an unglazed porcelain tile. If the mineral is very hard, crush a small amount of it off with a geological hammer, or rub it against a hard surface. Streak is more reliable in identification than the color of the mineral because it is more consistent.

Luster defines the way light is reflected off a mineral's exterior. The kind and intensity of luster vary according to the nature of the mineral surface and the amount of light exorbed. Well-recognized words used to describe luster are dull, metallic, pearly, glassy, greasy, and silky.