Properties and Uses

Identify the physical properties that can be used to identify common minerals Identify major elements in the Earth’s crust Explain the difference between rocks and minerals

Rocks and minerals are NOT the same thing! Think about how you use letters in the alphabet to make up words … minerals are the ABC’s and rocks are the words you make.

A naturally occurring, inorganic solid with a specific chemical composition and a definite crystalline structure Minerals play important roles in forming rocks and shaping Earth’s surface

Minerals must meet all five of the following criteria: 1. Naturally occurring … NOT MAN MADE 2. Solid … can not be a liquid or a gas 3. Inorganic … not made from anything that was once alive

4. A definite crystalline structure: A crystal is a solid in which the atoms are arranged in a repeating pattern There are six major crystal systems Cubic, tetragonal, hexagonal, orthorhombic, monoclinic, triclinic 5. A definite chemical composition: the elements that make it up are always the same and in the same proportions Example: Quartz (AKA silicon dioxide) For every 1 silicon atom (Si) there are two oxygen atoms (O) creating the molecule SiO2 No matter how much quartz you have it will ONLY be made up of SiO2

3,000 minerals are found in the Earth’s crust The most common of these minerals make up most of the rocks found in Earth’s crust About 90 known elements occur naturally in the crust The majority of all minerals are made up of the eight most common elements

Silicates Minerals containing silicon and oxygen along with one or more other elements (most common – feldspar and quartz) Make up 96% of the minerals found in Earth’s crust Carbonates Minerals composed of one or more metallic elements and the carbonate compound CO3 (most common – calcite and dolomite) Oxides Compounds of oxygen and metal (most common – hematite and magnetite)

Sulfides Compounds of sulfur and one or more other elements Sulfates Composed of elements with the sulfate compound SO4 Halides Made up of chloride or fluoride along with calcium, sodium, or potassium Native Elements Made up of one element only

Minerals have specific properties that are used to tell the difference between them By running different tests based on physical and chemical properties of a mineral, you can easily determine its identity NOTE: it is usually best to use a combination of tests rather than just one

Color: one of the most noticeable characteristics of a mineral but also the least reliable Streak: the color of a mineral when it is broken up and powdered Use a ceramic tile to test a minerals streak A minerals streak will not necessarily match a minerals external color

Texture: describes how a mineral feels to the touch Smooth, rough, greasy, glassy Luster: the way the surface of a mineral reflects light Two general types: metallic or non-metallic Other descriptions: dull, pearly, waxy, silky Cleavage/Fracture: describes the way a mineral sample is broken A mineral that splits easily and evenly has cleavage A mineral that breaks with rough/jagged edges has fracture

Cleavage Fracture

Hardness: a measure of how easily a mineral can be scratched One of the most useful tests for identifying minerals German geologist Friedrich Mohs developed a scale to test the hardness of a mineral

Density and Specific Gravity: Two minerals can be the same size but may feel quite different – one being heavier than the other due to a higher density. Example: pyrite has a density of 5.2 g/cm 3 and gold has a density of 19.0 g/cm 3 When density differences are too small to be distinguished you can measure density using specific gravity How much mass is in a given volume of water

Other properties: Some minerals have smell – sulfur Some minerals have taste – halite Some minerals are magnetic – magnetite Some minerals are fluorescent (show up under a black light) - fluorite

Minerals are virtually everywhere and have countless uses

A mineral is an ore if it contains a substance that can be mined at a profit Hematite, Magnetite, Pyrite  Iron materials Galena  Lead and Silver Bauxite  Aluminum materials Rutile  contains a titanium, a lightweight, durable metal often used in sports equipment

Ores that are located deep within Earth’s crust are removed my underground mining Ores located near the Earth’s surface are obtained from large, open-pit mines Minerals can be classified (or unclassified) as an ore based on its economic importance Depends on supply and demand and cost to mine vs. value of the ore

Extraction and processing has large environmental impacts in terms of such things as: Air quality Surface water quality Groundwater quality Soils Vegetation Aesthetics

Acid mine drainage is one example- sulfide minerals newly exposed to oxygen and water near the surface create sulfuric acid. Rainwater falling on the mine waste becomes acidified and can create toxic conditions in the runoff. This can release potentially dangerous heavy metals and kill organisms in the streams draining the mine waste.

A valuable mineral that is prized for its rarity and beauty Examples: Rubies Emeralds Diamonds Sapphires

Explain the difference between rocks and minerals. Identify the major elements in Earth’s crust by using Figure 4-4 on page 81 in your textbook to create a pie chart with a key. What mineral group do the two most abundant elements form? Identify the physical properties that can be used to identify common minerals? Which of these tests is least reliable? Which is one of the most useful? What is an ore? How does that differ from a gem?