Topic 11 Rocks and Minerals Minerals are economically

Topic 11 Rocks and Minerals

Minerals are economically important http: //www. mii. org/

Minerals • • Natural Solid Inorganic Definite chemical composition • Crystal structure due to internal arrangement of atoms

• There about 3000 known minerals • Minerals are made of elements (either a single element or a combination of elements) • Examples of Minerals – Native elements such as gold, a mineral made of one element (gold…Au) – Compounds such as calcite, a mineral made of 3 elements (calcium, carbon, and oxygen…Ca. CO 3) gold calcite

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

This is a siliconoxygen tetrahedron O 2 Si 4+ O 2 - Minerals that have both Silica and Oxygen are silicates which make up >70 % of continental crust - by weight

Positive ion The physical properties of a mineral are determined by its internal structure, or the arrangement of its atoms 2_26 b Shared oxygen ions Single chains

Positive ion 2_26 a Tetrahedron facing down Tetrahedron facing up Independent tetrahedra

The physical properties of a mineral are determined by its internal structure, or the arrangement of its atoms Silicate Minerals

Minerals are identified by their key characteristics • hardness • crystal shape (form) • luster • color • streak • cleavage/fracture • density (specific gravity) • special properties -reaction to acid -fluorescence -salty taste -magnetism

Mineral Hardness • Ability to scratch another mineral • Mohs scale from 1 (talc) to 10 (diamond) • Quartz (most common mineral and most dust particles) is 7

Mohs Mineral Hardness Scale 1) Talc Softest 2) Gypsum 3) Calcite 1 5 4) Flourite 5) Apatite 2 6) Feldspar 6 7) Quartz 8) Topaz 3 7 9) Corundum 10) Diamond 9 Hardest 4 8 10

Hardness: Based on Moh’s scale of hardness

Crystal Shape The shape a mineral takes if grown unimpeded Mineral Java Applet

Luster • Describes how light reflects off the surface • Main categories are “metallic” and “nonmetallic” • Non-metallic includes “dull, ” glassy, ” waxy, ” “pearly, ” and others

Luster: how a mineral reflects light Metallic Non-metallic

Color • results from ability to absorb some wavelengths and reflect others • some minerals have characteristic colors • others vary due to chemical differences or impurities (atoms mixed inside the main elements) • Color is not reliable

Streak • Color of the powder when rubbed on a “streak plate” (unglazed porcelain) • May be same as hand-specimen or different • Some paint is based on powdered minerals (streaks).

Streak: The powdered form of a mineral

Mineral cleavage/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

Cleavage & Fracture Best identified on a broken surface

Density (Specific Gravity) • All minerals have density (mass / volume), but some are very dense • Examples include galena, magnetite, and gold • Specific Gravity is the density of the mineral compared with density of water

Special Characteristics-the “Acid Test” Carbonates react with dilute HCl and other acids by fizzing or bubbling (releasing CO 2 gas)

Special Characteristics-Salty Taste • DO NOT TASTE MOST MINERALS! • Halite is the exception --it will taste salty

Special Characteristics-Magnetism • Many iron minerals will produce an invisible magnetic force field • “Lodestone” was used by Vikings more than 1, 000 years ago as compasses

Mineral Formation Minerals form 2 ways: 1. solidification of magma 2. precipitation of ions as water evaporates

That’s a lot of salt!!!!