An Introduction to Minerals

Atoms Atoms – basic building blocks for all earth materials; consist of 3 basic components: protons, neutrons, electrons

Atoms combine to form Elements Elements – fundamental component that can not be broken down into other substances by ordinary chemical processes Elements combine to form minerals

General Facts About Minerals 2,000 + minerals have been identified A few are “native elements” -- made of only one element, such as sulfur, gold. copper, and graphite (carbon) Most are compounds, especially the silicate group (Si, O). Other important groups are oxides, carbonates, and sulfides.

MINERALS NATIVE ELEMENTS Gold (Au) Silver (Ag) Gold Platinum (Pt) Diamond (C) Graphite (C) Sulfur (S) Copper (Cu) Gold Copper Silver

Mineral Criteria 1. Crystalline solid 2. Naturally occurring 3. Have a definite chemical composition 4. Inorganic

Minerals are identified by their Physical Properties Crystal Form Color Streak Luster – metallic, non-metallic Hardness – Moh’s Hardness Scale (1-10) Cleavage Fracture Specific Gravity Others

A mineral’s physical properties are controlled by its internal arrangement of atoms regularly repeating, orderly pattern

The most common crystalline structure Silica-oxygen tetrahedron – basic building block for silicate minerals

Silica tetrahedron combine several different ways Five major types of silicate minerals based on their structure Isolated tetrahedron Single chain C) Double chains D) Sheet silicates E) 3-D framework silicates

Minerals can have the same chemical composition (Carbon) but different physical properties because of their crystal structure Diamond Graphite

COLOR Color is not usually a definitive property of a mineral. Some minerals have characteristics colors Others vary due to chemical differences or impurities (atoms mixed inside the main elements) However most minerals have a variety of colors. The mineral sphalerite can be yellow, black, red, green or varieties thereof. Quartz is usually colorless, however it can have many colors depending on trace amounts of cations that substitute in the structure.

Some Colors of Quartz

STREAK For opaque minerals, if you rub the sample across a streak plate, it will leave a colored powder. This streak is distinctive for minerals and is used to identify minerals. Hematite can be brown, black, metallic gray and earthy but in all cases it gives a red-brown streak.

Varieties of Hematite – all same color streak

HARDNESS – Mineral’s resistance to scratching HARDNESS – Mineral’s resistance to scratching. Minerals with higher numbers will scratch minerals below The last three are not common minerals. Fingernail is 2 to 2.5, Cu penny is around 3.5; hammer is about 5.1, knife is 5.2 and plate glass is 5.5.

LUSTER Metallic does not mean shiny Describes how light reflects off the surface Categories: Metallic or non-metallic Metallic does not mean shiny Non-metallic: vitreous or glassy; silky; resinous; pearly; greasy; waxy, dull; earthy

Examples of metallic luster

More Examples of Metallic Luster Pyrite (FeS2) Galena (PbS) PYRITE GALENA

Example of non-metallic luster Vitreous--quartz

Example of non-metallic luster Silky--example plagioclase feldspar

Non-metallic and metallic luster – earthy hematite – metallic hematite

Cleavage and Fracture Some minerals split along flat surfaces when struck hard--this is called mineral cleavage Other minerals break unevenly along rough or curved surfaces--this is called fracture A few minerals have both cleavage and fracture ( mica )

Cleavage Halite (NaCl) Fluorite (CaF2) HALITE FLUORITE

Cleavage MUSCOVITE BIOTITE

Rose Quartz – Conchoidal Fracture

Conchoidal Fracture - Quartz Obsidian

DENSITY / SPECIFIC GRAVITY This is the ratio of the density of the mineral to the density of water. Weight Air/(Weight Air-Weight in water) = specific gravity It is obtained by weighing a piece of mineral in air and then in water. The difference in weight is equal to the volume of water displaced.

Acid Test for Carbonates Special Characteristics: Carbonates react with dilute HCl and other acids by fizzing or bubbling (releasing CO2 gas)

MINERALS NONSILICATE MINERALS CARBONATES Carbonate ion (CO32-) is prominent in minerals. Has -2 charge. Combines readily with positive ions. Bonds generally weak. Minerals are soft (3-4). Minerals are soluble in acidic water. Leads to cave development. Calcite (CaCO3) Dolomite (CaMg(CO3)2) CALCITE DOLOMITE

Less than a dozen are common in most rocks Quartz Feldspar (group) Muscovite (silver white mica) Biotite (black mica) Calcite Pyroxene Olivine Amphibole (group) Magnetite, limonite, and other iron oxides Pyrite

Common uses include: Aluminum--packaging, transport, building Beryllium--gemstones, fluorescent lights Copper--electric cables, wires, switches Feldspar--glass and ceramics Iron--buildings, automobiles, magnets Calcite--toothpaste, construction