BASIC GEOLOGY Chapter 2 : Atoms to Minerals

Normal Matter is composed of……. Atoms

But not all atoms are the same! Atoms differ in the number of “pieces” ( Protons, Neutrons and Electrons) that they have inside of them.

Atoms with certain consistent characteristics are called…. Elements

An Element is... matter that is made up of atoms (or one atom) that have the same number of Protons in their nucleus. matter that is made up of atoms…

Not all atoms of the same element are the same, either. But!!! Not all atoms of the same element are the same, either.

Atoms of the same element that have different numbers of neutrons in their nuclei are called…. Isotopes

Certain isotopes of elements are unstable, or radioactive Certain isotopes of elements are unstable, or radioactive. (example: Carbon-14 and Uranium-238) These radioactive isotopes of elements allow us to do absolute-age dating!

Most substances on Earth are not pure elements but rather…. ??? Compounds

What is a Compound?

A Compound is….. A substance made from two or more different elements that have been chemically combined.

A Mixture, on the other hand, is… A substance made from two or more different elements that have not been chemically combined, and which can be separated by physical means

Mixtures

Elements by themselves are much less common than Compounds, because they tend to combine with each other to form Compounds.

Elements and Compounds in their solid form make up… Minerals

What is a Mineral??? What is a Mineral?

A Mineral is a naturally occurring Inorganic Solid with a definite chemical composition and a crystalline structure.

That means that… It can’t be organic in origin It can’t be a liquid and.. It has to have a crystal structure

Lets put that in a list format. 1. Minerals are a naturally occurring substance. 2. Minerals are solids. 3. Minerals have a definite chemical composition.

4. The atoms that make up minerals are arranged in an orderly pattern (They form crystals). 5. Minerals are inorganic. (They were never alive.)

How many different minerals are there on Earth??? Answer: About 4,000

More than 90% of all of the minerals in the Earth’s Crust, however, are made up of compounds containing Silicon and Oxygen, the two most abundant elements on Earth.

The percent composition of Silicate And….. The percent composition of Silicate Minerals in an igneous rock determine a lot of the characteristics of that rock and the magma that formed it.

High Silica content forms light-colored rocks.

While lower (but only by about 25%) Silica content forms darker-colored rocks.

How do Minerals Form??? 1. Minerals form in cooling magma chambers

Different types of minerals crystallize at different temperatures Decreasing temperature Bowen’s Reaction Series Mineral formation in a Magma Chamber

Olivine

Pyroxene

Peridotite- Mostly Olivine

Gabbro- Pyroxene and Olivine

Andesite- Hornblend and Biotite? and Plagioclase Feldspar

Potassium Feldspar

Quartz

Pink Granite

Mineral Fractionalization in a Magma Chamber

2. Metamorphic Minerals: Some minerals occur as the result of Recrystallisation and Reaction within existing rocks which produces new minerals in response to changes in Pressure and Heat

3. Some types of minerals form as water containing dissolved ions slowly evaporates. Salt deposits

How long does it take for minerals to form?? Minerals in solution in water can form relatively quickly when the water evaporates. Minerals in magma can form as quickly as the magma/lava can crystallize (lava can cool in minutes, while magma can take thousands of years).

Crystalline Structure Minerals have a Crystalline Structure

A regular geometric solid with smooth surfaces called…. A Crystal is…. A regular geometric solid with smooth surfaces called…. Crystal Faces

The orderly arrangement of ions, molecules, or atoms, in any mineral determines the shape of its crystals.

Although there are thousands of different types of minerals, their crystals come in six basic types of shapes

Cubic

Orthorhombic

Tetragonal

Triclinic

Hexagonal

Monoclinic

Physical Properites of Minerals

With all of the different types of minerals, how do you identify them??

Luster Hardness Streak Cleavage Minerals are identified and classified by visual inspection, and by performing simple tests to determine their physical properties Color Specific Gravity Fracture

Rock-Forming Minerals

Only 30 of the 4,000 known minerals are common. These 30 minerals are known as the rock-forming minerals Rock-Forming Minerals.

Most rock-forming minerals are… Silicates The percent composition of Silicate minerals in a rock determines the type of rock it is.

Rocks that have a high percentage of Silicates are light in color, and are called Felsic rocks.

Rocks that have a low percentage of Silicates are dark in color, and are called Mafic rocks.

Rocks are often made of several different minerals.

Identifying Minerals by Inspection

Minerals are most often identified by inspecting their Physical and Chemical properties.

Color Color is the most easily observed, but least reliable property of a mineral for identification. This is because the color of many minerals varies with the kind of impurities in the mineral.

Luster Luster is the way in which a mineral shines in the light.

Types of Luster

Streak Streak is the color of the powder left on a streak plate when a mineral is rubbed on it. Streak is much more reliable than color because, although the color of a mineral changes, its streak does not.

Cleavage Cleavage is the tendency of a mineral to split in a particular direction.

“Sheety” Cleavage

Feldspars always cleave readily at or near right angles.

Fracture Fracture is the tendency of a mineral to break in directions other than along crystal faces or cleavage surfaces.

Conchoidal or shell-like fracture Fibrous facture

Hardness Hardness is the resistance of a mineral to being scratched. The Mohs Hardness Scale is one of the most effective tool for identifying minerals.