Minerals

What is a mineral? A mineral is a naturally occurring, inorganic solid with an orderly crystalline structure and a definite chemical composition

5 Characteristics of Minerals 1. Naturally occurring- forms by natural geologic processes, synthetic gems are not considered minerals 2. Solid Substance- within temperature ranges that occur at Earth’s surface 3. Orderly crystalline Structure- atoms are arranged in an orderly and repetitive manner 4. Definite Chemical Composition- minerals are chemical compounds made up of a two or more elements (exception- native elements) 5. Generally Considered Inorganic- table salt is inorganic, sugar is organic and is not a crystal. Sugar comes from a plant Calcium carbonate- secreted by marine animals, inorganic or organic?

How do minerals form? Four major processes by which minerals form 1. Crystallization from magma 2. Precipitation 3. Pressure and Temperature 4. Hydrothermal Solutions

Crystallization of Magma Magma is molten rock that occurs deep within the Earth As magma cools, elements combine to form minerals First minerals formed are rich in iron, calcium, magnesium Next are minerals rich in sodium, potassium, and aluminum

Precipitation Minerals form when water evaporates in lakes, rivers, ponds, and oceans Minerals are left behind or precipitated from the water Halite and calcite form this way

Pressure and Temperature Some minerals from when others are subject to changes in pressure and temperature Atoms are rearranged to form more compact minerals Talc and muscovite are formed this way

Hydrothermal Solutions Hydro (water) thermal (heat) Very hot mixtures of water and dissolved substances Can have temperature between 100oC and 300oC Chemical reactions occur at these temperatures causing minerals to form, or as solution cools minerals form

Mineral Groups There are over 3800 named minerals on Earth and more are identified each year Common Minerals are classified into groups based on their composition Seven mineral groups- Silicates, carbonates, oxides, sulfates, sulfides, halides, native elements

Silicates These are the most common- remember from chemistry unit, the most abundant elements in Earth’s crust are oxygen and silicon Silicon-oxygen tetrahedron- structure which consists of one silicon to four oxygen molecules (most silicates occur in this form) Most silicate minerals form from crystallization of magma near or far below earth’s surface Examples include- quartz, augite, micas

Carbonates Second most abundant mineral group Contain carbon, oxygen, and one or more other metallic elements Examples include calcite, dolomite, limestone, marble

Oxides Oxides contain oxygen and one or more other elements, which are usually metals Some form under Earth’s surface from crystallization of magma (rutile), others from when minerals are subject to changes in temperature and pressure (corundum), others form when a mineral is exposed to liquid water (hematite, iron oxide)

Sulfates and Sulfides Both contain sulfur Sulfates- (anhydrite, and gypsum) form when mineral rich waters evaporate Sulfides- (galena, sphalerite, pyrite) form from hydrothermal solutions

Halides This group contains a halogen ion plus one or more other elements Halogens occur in group 17 (7a) of the periodic table Examples include- halite and fluorite

Native Elements This group occurs in pure elemental form Examples include- gold, silver, copper, sulfur, carbon (graphite and diamonds)

Properties of Minerals and Mineral Identification Properties of minerals are determined by composition and structure Color Streak Luster Crystal Form Hardness Cleavage Fracture Density Unique properties include- magnetism, double refraction, chemical reactions with HCl

Color and Luster Color can be unique to some minerals, but for most it is not the most useful for identification Color within minerals can vary depending on other elements present within the mineral Luster- how light is reflected from the surface of a mineral Metallic (metal like), vitreous/glassy (quartz), pearly, silky, earthy

Streak and Crystal Form Color of a mineral in its powdered form We can use a streak plate (a sheet of unglazed porcelain) to determine this property Crystal form- visible expression of internal arrangement of atoms When a mineral forms without any space restrictions it will develop into a perfect crystal with well developed faces 6 Crystal Forms

Type 1: Isometric (Cubic) 6 sides All sides are square Examples *pyrite *halite *diamond *galena

Type 2: Tetragonal 6 sides 4 rectangles, 2 squares (right angles) Example *zircon

Type 3: Hexagonal 8 sides 2 hexagons, 6 rectangles (right angles) Examples *ice *quartz *emeralds

Type 4: Orthorhombic 6 sides 6 rectangles (3 pairs of rectangles with different sizes at right angles) Examples *topaz *barite

Type 5: Monoclinic 6 sides 4 rectangles, 2 parallelograms (several angles) Examples *gypsum *muscovite

Type 6: Triclinic 6 sides Parallelograms (no right angles) Example *turquoise

Mineral with a Cubic or Isometric Crystal Shape Pyrite has a Cubic Crystal Structure

Mineral with a Tetragonal Crystal Shape Rutile has a Tetragonal Crystal Structure

Mineral with a Hexagonal Crystal Shape Ruby has a Hexagonal Crystal Structure

Minerals with Orthorhombic Crystal Shapes The is a very big crystal system containing gemstones such as topaz, peridot, tanzanite, and many others

Mineral with a Monoclinic Crystal Shape Gypsum is a mineral with a Monoclinic Crystal Structure

Mineral with a Triclinic Crystal Shape Calcite- Triclinic crystal look like a rectangular box that someone pushed from one side to make it lean

Hardness One of the more useful properties for identification Done by rubbing two minerals together, one will scratch the other unless they have the same hardness Mohs Hardness Scale- 1-10 Talc is the softest, what is hardest?

Moh’s Hardness Scale

Cleavage and Fracture Cleavage is the tendency of a mineral to cleave or break along flat, even surfaces Fracture is what happens to all other minerals that do not display cleavage Fracture can be described as the uneven breakage of a mineral Internal atomic structure determines whether a mineral will display cleavage or fracture

Fracture or Cleavage? Selena

Density Ratio of an objects mass to its volume D= M/V For minerals we would use g/cm3, since we are looking at solids Density of pure minerals are of constant value. Therefore we can use density to identify pure minerals or to tell if a mineral is not in pure form.

Other Properties Magnetism- some types of magnetite are magnetic and can be used to pick of metal objects Double Refraction- When calcite is placed over printed words the letters appear doubled Chemical Reactions with HCl- Carbonate minerals will fizz when they come into contact with hydrochloric acid

Double Refraction of Calcite

Magnetism