MINERALS!

Earth’s Geosphere

• Densest part of planet’s materials; solid at surface temperatures; includes rocks and minerals

• Accounts for ___% of Earth’s matter by volume• 3 major compositional layers of geosphere

formed through differentiation– Core, mantle, crust – Focus of this unit is on crust

• Composed primarily of 8 elements

Diamonds and Graphite• Why do they have such

different properties?– Same composition!– Both minerals!– Arrangement of atoms

• Why is one common and the other rare?

• Need to understand the basic building blocks of matter, and how minerals form and get their physical characteristics

Let’s talk elements, atoms, isotopes, compounds, and molecules. • An element is the most basic substance into which matter can be

separated. • Cannot be decomposed or changed into other substances except

by the means of radioactive decay.• Atoms are the smallest, most complete forms of an element.

• Isotopes are atoms that have the same atomic number, but have a different atomic mass (or weight).

• Compounds are formed from combining one or more elements (or, more specifically, the atoms of more than one element) in a specific ratio. • Elements are held together by a force called a bond. • Combining 2 or more elements creates compounds with different

properties than their elements!• Molecules have all the properties of a particular compound, and

consist of two or more atoms of different elements.

Minerals, by definition, are naturally occurring, inorganic elements or compounds having an orderly internal structure and characteristic chemical composition, crystal form, and physical properties.

On the other hand, two or more elements can bond to form a mineral. An example of this is quartz (SiO2):

We can have minerals made up of just one element. An example of this is gold (Au):

So what’s a ROCK…..?•It’s a naturally formed, coherent aggregate of minerals•Can consist of crystals of more than one mineral, or can even be made up of multiple crystals of the same mineral.•Minerals combine under different physical conditions to form rocks. There are three main categories of rocks: igneous, sedimentary, and metamorphic.

Classification of Minerals

• Based on composition. • Classes are Silicates and Non-Silicates,

which include…..(1) Carbonates(2) Oxides(3) Sulfates/sulfides(4) Halides(5) Native elements

Silicate Minerals• Silicon Oxygen (SiO2) tetrahedron --> important

building block for SILICATES!• Silicate minerals make up over 95% of all rocks

Common Minerals

• Less than 20 of the thousands of minerals are common

• Minerals made with silicon and oxygen are the most common (silicate minerals)

• Common Rock forming minerals are:– Quartz, feldspar, muscovite

and biotite (micas), hornblende (amphibole) and pyroxene, olivine

– Calcite, gypsum, halite, hematite

How do minerals form?• Crystallization

– In hot magma, atoms are not bound in crystal form. As magma cools the atoms arrange themselves into crystalline structures forming minerals!

– Happens underground or at the surface in volcanically active places• Evaporation/Precipitation

– Atoms can be dissolved in solutions of water. If water evaporates or changes temperature or gets too many atoms in it the dissolved atoms may form crystalline solids…minerals!

– Happens at bottom of bodies of water, especially where there is volcanically heated hot water dissolving minerals and then cooling when it touches other water or air.

• High Temperatures and or Pressures– Without melting can cause new minerals to form as atoms rearrange to form

more compact or otherwise stable arrangements

Mineral Characteristics

• Minerals can be identified based on characteristics such as– Color, crystal shape, hardness, density– Streak, fracture vs. cleavage plane, luster,

reaction to acid, magnetism

• These characteristics are caused by– The type of elements in the mineral– The arrangement of those elements

Color

• Some minerals come in more than 1 color…

Streak

• There are many minerals with the same color…how do you tell them apart?

No matter what color a sample of hematite is, it has a red-

brown streak!

Streak is useful for dark, metallic minerals that are not very hard

What are the two major kinds of Luster?

• Metallic and non-metallic• Which has metallic luster?

Crystal Shapes

Quartz

Quartz breaks irregularly

• “fracture”

Mica breaks in flat sheets

• Weak cleavage plane in 1 direction

Cleavage

• Due to planes of weaknesses in the atomic structure

Mohs Scale of Hardness: “Scratch test”

What mineral property test is this?

Rocks Minerals Both neither

A substance that cannot be broken down into simpler substances by chemical or physical means

The smallest paticle of matter that contains the characteristics of an element

Naturally occurring, inorganic solid

Orderly crystalline structure and definite chemical composition. Will form characteristic external crystal shape if given the space

Classified into categories based only on composition and arrangement of atoms

Always composed of more than one mineral

Classified into categories based on how it formed

May dissolve or react to acids

Never has cleavage planes