Minerals A mineral must: 1.Occur naturally 2.Be a crystalline solid 3.Have a definite chemical composition 4.Possess characteristic physical properties 5.NOT be organic

Why aren’t the following minerals? Water Glass

Why aren’t the following minerals? Water – it is a liquid at room temperature Glass – It is not naturally occurring

Why aren’t the following minerals? Coal

Why aren’t the following minerals? Coal – It is organic – It lacks a definite chemical composition – It does not have repeating structure

The Most Common Elements in the Earth’s Crust 1.Oxygen 2.Silicon 3.Aluminum 4.Iron 5.Calcium 6.Sodium 7.Potassium 8.Magnesium These eight elements make up 98.5% of the Earth’s crust. Almost 94% of the crust’s volume (not mass) is oxygen.

Elements are not distributed evenly throughout the layers. Not in your notes.

How Minerals Form Atoms in magma move about. As the magma cools, movement slows and the atoms move closer together. They bond chemically. The rate at which the magma cools determines the size of the mineral grains. Dissolved atoms chemically link as water evaporates.

COMMON MINERAL GROUPS There are seven basic nonsilicate mineral groups. More than 90% of the minerals in the crust and mantle are silicates.

1.Native Elements do not combine with other elements in nature. Gold (Au) Silver (Ag) Platinum (Pt) Diamond (C) Graphite (C) Sulfur (S) Copper (Cu) NONSILICATE MINERALS Copper Silver Gold

The two most abundant elements, silicon and oxygen combine to form the basic building block for most common minerals. Four oxygen atoms are packed together around a single silicon atom. A silica tetrahedron is the result. SILICATE MINERALS

Silica tetrahedron Half the bonds are ionic. Half the bonds are covalent. It has an overall negative charge. Tetrahedrons can link together in different ways.

Silicates Combinations of oxygen and silicon plus one other metallic element are called silicates. They can exist independently, or as single chains, double chains, sheets, or frameworks.

Silica Tetrahedron (blue = silicon; brown = oxygen) 4 oxygen anions are bonded to a single silicon cation. Silicon is positively charged (+4) Oxygen is negatively charged (-2) Net charge on tetrahedron: -4 Not in your notes.

Single Tetrahedron Olivine Two atoms of magnesium or iron balance the negative charge. X 2 SiO 4

Single Chain Pyroxene Note the fibrous appearance. XSiO 3 One atom of iron, magnesium, aluminum, or calcium balance the negative charge.

Single Chain Silicates Adjacent tetrahedrons form a chain by sharing 2 of their oxygen with neighboring tetrahedrons. E.g. pyroxenes (mafic silicates) Not in your notes.

Double Chain Amphibole XSi 8 O 22 (OH) 2 A combination of calcium, sodium, iron, magnesium, and aluminum balance the negative charge.

Double Chain Silicates Two chains can link up by sharing oxygen. E.g. amphiboles (mafic silicates) Not in your notes.

Sheet Micas – Biotite – Muscovite KXAlSi 3 O 10 (OH) 2 A magnesium, iron, and aluminum balance the negative charge in biotite. In muscovite only aluminum balances the negative charge.

Sheet Silicates Sheets are formed when each tetrahedron shares 3 of its oxygen with neighbors. E.g. micas, clay minerals Not in your notes.

Framework feldspar KAlSi 3 O 8 = orthoclase feldspar a.k.a. potassium feldspar

Framework Silicates Every oxygen in each tetrahedron is shared to a form 3-D framework. E.g. feldspar, quartz (non-mafic silicates) Not in your notes.

Identifying Minerals

Mineral properties Colour Luster Habit (Shape) Cleavage & Fracture Streak Hardness

Colour: (Not mineral specific)

Quartz comes in a variety of colours Not in your notes.

Luster: How minerals reflect light Non- metallic Metallic Metallic luster does not have to be shiny – It can look like a broken iron rod.

Mineral Habit (Shape) Shape a mineral takes if grown unimpeded

Cleavage & Fracture Cleavage: planes or surfaces of weakness along which minerals can break Fracture: surfaces other than cleavage planes along which minerals can break

Examples of Cleavage Not in your notes.

Cleavage & Fracture and resulting crystal shape Not in your notes.

Fracture Some minerals do not have cleavage but do show a characteristic fracture. Fractures (irregular breaks) can sometimes be distinctive When the fracture results in smooth, curved surfaces, the sample is said to exhibit “conchoidal” fracture

Quartz has conchoidal fracture Not in your notes.

Crystalline Structure A crystal is a regular geometric solid with smooth surfaces called crystal faces. The orderly arrangement of ions determines the shape of the crystal. There are six basic crystal shapes

Streak: The powdered form of a mineral when rubbbed on an unglazed tile.

Hardness: Is the resistance of a mineral to abrasion or scratching. Geologists use Moh’s scale of hardness.

If this were an absolute scale diamond would have a value of 40.

As an example, calcite will scratch gypsum and talc but not fluorite, apatite, or any of the others. The hardest substance also produces the softest substance, graphite.

Other Properties Specific gravity Reaction to acid Striations Magnetism