The Basics and Minerals 1

Mineral

Naturally occurring solid substances that are homogenous and inorganic, consisting of various elements and compounds arranged in a defined chemical composition and characteristic crystalline structure. Minerals are the building blocks of rocks and exhibit specific physical and chemical properties.

Rock

A coherent and solid aggregate composed mainly of minerals or mineraloids that forms the Earth's crust. Rocks can be classified into three primary types: igneous rocks, formed from cooled magma; sedimentary rocks, created from compressed sediments; and metamorphic rocks, changed by heat and pressure.

Luster

The appearance or quality of light reflected from a mineral's surface, which helps to determine its identity. Luster is categorized primarily into two types: metallic, where light reflects like a polished metal, and nonmetallic, which may appear glassy, dull, waxy, or silky.

Nonmetallic Luster

A type of luster where light can penetrate and reflect from within the mineral, giving it a range of appearances such as vitreous (glassy), resinous (plastic), waxy, or earthy (dull). These variations in luster provide insight into the mineral's composition and structure.

Metallic Luster

A distinctive luster characterized by a bright, shiny surface that reflects light like metal. In minerals with metallic luster, light does not enter the crystalline structure; instead, it is reflected off the outer surface, giving a hard, glimmering appearance.

Streak

The color of a mineral when it is ground to a fine powder, tested by rubbing the mineral across an unglazed porcelain streak plate. The streak can vary from the color of the mineral itself and serves as a valuable diagnostic tool for mineral identification.

Hardness

A quantitative measurement of a mineral's resistance to being scratched, graded on the Mohs scale from 1 (softest) to 10 (hardest). This property helps to categorize minerals based on their ability to withstand abrasion and wear.

Cleavage

The tendency of a mineral to break along flat surfaces or planes that correspond with its crystal structure, resulting in smooth, planar facets. A distinctive property used in mineral identification, often described by the number and angles of these planes.

Fracture

The type of breakage exhibited by a mineral when it does not split along a cleavage plane. Characterized by irregular, unpredictable patterns, which can be described as conchoidal (smooth curved surfaces) or uneven.

Crystal Faces

The flat, smooth surfaces that form the outer boundary of a crystal and correspond to the mineral's internal atomic arrangement. Crystal faces are integral to identifying the mineral's shape and symmetry.

Taste (Mineral Feature)

A sensory property where certain minerals, such as halite, have a distinctive flavor, often described as salty due to its chemical similarity to table salt (sodium chloride). This property can assist in identifying some minerals.

Smell (Mineral Feature)

The scent associated with certain minerals, notably sulfur, which is recognizable for its strong odor reminiscent of rotten eggs. This characteristic olfactory property can aid in the identification of minerals.

Reactivity (Mineral Feature)

The capability of a mineral, such as calcite, to undergo chemical reactions with substances like hydrochloric acid (HCl), resulting in observable fizzing or effervescence. This reactivity is crucial for distinguishing certain minerals in the field.

Magnetism (Mineral Feature)

The property exhibited by some minerals, like magnetite, that allows them to attract or repel other magnetic materials. This characteristic can be tested using a magnet and is a key identifier for specific minerals.

Specific Gravity

The ratio of a mineral's weight compared to the weight of an equal volume of water, providing a measure of its density. For example, galena is noted for being heavy and dense, often aiding in mineral identification based on this property.

has cleavage, white streak, vitreous luster, 6, white pink or reddish

orthoclase feldspar

no cleavage, white streak, clear, pink, smoky, vitreous luster

quartz

rhombohedral cleavage, white or clear, white streak, reacts with acid, 3, vitreous luster

calcite

• Hardness: 6-6.5

• Luster: Vitreous

• Cleavage: Two directions at nearly 90°

• Color: White, gray, or bluish

plagioclase feldspar

• Hardness: 2.5

• Luster: Vitreous

• Cleavage: Cubic

• Color: Colorless or white

• Streak: White

halite

• Hardness: 2.5

• Luster: Metallic

• Cleavage: Cubic

• Color: Silver-gray

• Streak: Gray

galena

• Hardness: 5.5-6.5

• Luster: Metallic

• Cleavage: None

• Color: Black

• Streak: Black

magnetite

• Hardness: 4-5.5

• Luster: Earthy to dull

• Cleavage: None

• Color: Yellow-brown

• Streak: Yellowish-brown

limonite

• Hardness: 6.5-7.5

• Luster: Vitreous

• Cleavage: None (fractures)

• Color: Red, green, brown, yellow

• Streak: White

garnet

• Hardness: 2.5-3

• Luster: Vitreous to pearly

• Cleavage: One perfect direction (sheet-like)

• Color: Black or dark brown

• Streak: White to gray

biotite

• Hardness: 2-2.5

• Luster: Vitreous to pearly

• Cleavage: One perfect direction

• Color: Colorless to light brown

• Streak: White

muscovite

• Hardness: 6.5-7

• Luster: Vitreous

• Cleavage: Poor

• Color: Green

• Streak: White

olivine

• Hardness: 5-6

• Luster: Vitreous to dull

• Cleavage: Two directions at nearly 90°

• Color: Dark green to black

• Streak: White to gray

pyroxene

• Hardness: 5-6

• Luster: Vitreous to dull

• Cleavage: Two directions at 60° and 120°

• Color: Dark green to black

• Streak: White to gray

amphibole

• Hardness: 1 (softest mineral)

• Luster: Pearly

• Cleavage: Perfect in one direction

• Color: White to green

• Streak: White

talc

• Hardness: 1-2

• Luster: Metallic to dull

• Cleavage: Perfect in one direction

• Color: Gray to black

• Streak: Black

graphite

• Hardness: 5-6

• Luster: Metallic to earthy

• Cleavage: None

• Color: Reddish-brown to black

• Streak: Red to reddish-brown

hematite

• Hardness: 1.5-2.5

• Luster: Resinous to dull

• Cleavage: Poor

• Color: Bright yellow

• Streak: Yellow

sulfur

• Hardness: 6-6.5

• Luster: Metallic

• Cleavage: None

• Color: Brass-yellow

• Streak: Greenish-black

pyrite

• Hardness: 4

• Luster: Vitreous

• Cleavage: Perfect in four directions

• Color: Various (purple, green, blue, yellow)

• Streak: White

fluorite