Topic 11 Rocks and Minerals

Minerals are economically important

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

There are 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…CaCO 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

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

2_26b Single chain Shared oxygen ions Positive ion Single chains The physical properties of a mineral are determined by its internal structure, or the arrangement of its atoms

2_26a Tetrahedron facing down Tetrahedron facing up Positive ion 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 2) Gypsum 3) Calcite 4) Flourite 5) Apatite 6) Feldspar 7) Quartz 8) Topaz 9) Corundum 10) Diamond Softest Hardest

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 “non- metallic” Non-metallic includes “dull,” glassy,” waxy,” “pearly,” and others

Non- metallic Metallic Luster: how a mineral reflects light

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!!!!