Minerals Why are we studying crystals? Crystals make up minerals Minerals make up rocks Rocks make up the Earth ….aaaannndd this is Geo(earth)science.

Minerals

Why are we studying crystals?

Crystals make up mineralsMinerals make up rocksRocks make up the Earth

….aaaannndd this is Geo(earth)science

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What is a mineral? A mineral is a naturally occurring,

inorganic solid with an orderly crystalline structure and a definite chemical composition

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WHY STUDY MINERALS? FOUND IN/USED IN MAKING ALMOST

EVERYTHING! HOUSES AND APPLIANCES MEDICATIONS FOOD FLAVORINGS JEWELRY COMPUTERS/PHONES

All electronics contain at least 30 minerals

If it wasn’t grown, it was mined!

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

5 Characteristics of Minerals 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

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Different types of minerals crystallize at different temperatures

Decreasing temperature

Mineral formation in a Magma ChamberBowen’s Reaction Series

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

The Naica Mine of Chihuahua, Mexico, is a working mine that is known for its extraordinary crystals. Naica is a lead, zinc and silver mine in which large voids have been found, containing crystals of selenite (gypsum) as large as 4 feet in diameter and 50 feet long. The chamber holding these crystals is known as the Crystal Cave of Giants, and is approximately 1000 feet down. The crystals were formed by hydrothermal fluids emanating from the magma chambers below.

Largest Selenite Crystals In The

World

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He said that the sight was beautiful “…like light reflecting off a broken mirror”. The translucent crystals lie pitched atop one another, as though moonbeams suddenly took on weight and substance. One month later, another team of Naica miners found an even larger cavern adjacent to the first one.

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These mountains are 200 million year old limestone massifs hosting networks of caves crossed by very deep hot and mineralized thermal waters. When these waters reached the relatively colder and closer to the surface environments they deposited much of their salt content as lead,zinc and silver .

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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

Of the almost 4000 known minerals, only about 30 are common.

The most common are quartz, feldspar, mica, and calcite.

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Mineral Chemistry (Main Mineral Groups)

• Continental crustal chemistry:

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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

Silicon-Oxygen Tetrahedron

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)

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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 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

Color

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Pure quartz is colorless or white, impurities can make the mineral rose, purple or pink!

LusterLuster- how light is reflected from

the surface of a mineral Metallic (metal like), vitreous/glassy

(quartz), pearly, silky, earthy

Metallicexample:Galena

Non-metallicexample:

Orthoclase

Luster Some other ways to describe luster are Dull - just a non-reflective surface of any kind Earthy - the look of dirt or dried mud Fibrous - the look of fibers Greasy - the look of grease Gumdrop - the look a sucked on hard candy Metallic - the look of metals Pearly - the look of a pearl Pitchy - the look of tar Resinous - the look of resins such as dried glue or

chewing gum Silky - the look of silk, similar to fibrous but more

compact Submetallic - a poor metallic luster, opaque but

reflecting little light Vitreous - the most common luster, it simply means the

look of glass Waxy - the look of wax

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Streak 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 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

Mineral with a Cubic or Isometric Crystal Shape

Pyrite has a Cubic Crystal Structure

Type 2: Tetragonal6 sides4 rectangles, 2

squares (right angles)

Example*zircon

Mineral with a Tetragonal Crystal Shape

Rutile has a Tetragonal Crystal Structure

Type 3: Hexagonal8 sides2 hexagons, 6

rectangles (right angles)

Examples*ice*quartz*emeralds

Mineral with a Hexagonal Crystal Shape

Ruby has a Hexagonal Crystal Structure

Type 4: Orthorhombic6 sides6 rectangles (3

pairs of rectangles with different sizes at right angles)

Examples*topaz*barite

Minerals with Orthorhombic Crystal Shapes

The is a very big crystal system containing gemstones such as topaz, peridot, tanzanite, and many others

Aragonite

Type 5: Monoclinic6 sides4 rectangles, 2

parallelograms (several angles)

Examples*gypsum*muscovite

Mineral with a Monoclinic Crystal Shape

Gypsum is a mineral with a Monoclinic Crystal Structure

Type 6: Triclinic6 sidesParallelograms

(no right angles)Example

*turquoise

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?

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?

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

Magnetism

Other Properties Double Refraction- When calcite is

placed over printed words the letters appear doubled

Double Refraction of Calcite

Other Properties Chemical Reactions with HCl- Carbonate

minerals will fizz when they come into contact with hydrochloric acid