The Basics and Minerals 1

Mineral: components of rocks

• naturally occurring

• homogenous

• inorganic solid substance

• has a definite chemical composition

• characteristic crystalline structure

rock: three types - igneous, sedimentary, metamorphic

• any aggregate of minerals or materials that makes up the earths crust

• may be unconsolidated (loose) such as a sand, clay or mud, or consolidated (solid) such as granite, limestone, or coal

luster: the way light is reflected from a mineral

Nonmetallic: light can pass into and be reflected from within it (see-through), looks glassy, plastic, waxy, dull (doesn’t look like a metal)

metallic: no light at all can penetrate the crystalline structure, so all the reflected light comes from the surface, resulting 9usually) in a ‘hard’ glint or glitter, like a metal

streak: the color of a mineral when powdered. it can be observed by scratching the mineral on a porcelain plate, called a streak plate.

• minerals harder than porcelain have no streak

hardness: measure of how resistant a substance is to being scratched. some minerals have ranges oof hardness instead of one singular value.

• if the mineral scratches the glass plate, but leaves a streak on the streak plate, that mineral has a hardness between 5.5 and 6.5

• if you can’t scratch the mineral with your fingernail but you can scratch it with a penny, that mineral is between 2.5 and 3.5

• streak plate - 7

• steel nail - 6.5

• glass - 5.5

• penny - 3.5

• fingernail - 2.5

cleavage: the planes along which a mineral tends to break

• cleavage planes are always parallel to a crystal face

• ex: biotite has two crystal faces that are parallel meaning it has cleavage in ONE DIRECTION (basal)

fracture: any break that is not along a cleavage plane

• most fracture surfaces are irregular

• some will break along smooth, curved, and slightly rippled surfaces called conchoidal (ex: quartz)

crystal faces/form: form a mineral takes when it grows in open space

• the smooth, planar surfaces that define the shape of a crystal and reflect its internal atomic structure

• cleavage planes are always parallel to a crystal face, but a crystal face is not always a cleavage plane

other features:

• taste - halite tastes salty (same chemical formula as table salt)

• smell - sulfur smells like rotten eggs

• reactivity - calcite reacts with HCI acid

• magnetism - magnetite

• specific gravity - relative weight of a mineral ex: galena is heavy/dense