Minerals and Rocks 5 Characteristics of Minerals Naturally

Minerals and Rocks

5 Characteristics of Minerals • • • Naturally Occurring Inorganic Found as a solid in nature Formed from elements or compounds Definite chemical make up and regular atomic structure

By that definition… • Is a snow flake a mineral?

A. • Minerals are classified according to their physical and chemical properties.

Physical Properties • 1) Color: easiest to recognize but not very reliable – Example: quartz- comes in several different colors – Example: calcite and halite- both can be transparent and/or same color

Physical Properties • 2) Streak- the color of a mineral when powdered – Test: rub the mineral across a piece of unglazed ceramic tile

Physical Properties • 3) Luster: the way a mineral reflects light – Metallic- looks like shiny metal – Non-Metallic- does not look like shiny metal (can be dull, waxy, glassy, etc)

Physical Properties • 4) Hardness: a minerals ability to scratch or be scratched – Test: Use an edge of your mineral and try to scratch a glass plate – Moh’s hardness scale: 10 common minerals placed in order of hardness • The higher the number the harder the mineral

Physical Properties • 5) Cleavage: the tendency of a mineral to split along smooth, flat surfaces called plains – Test: Look at the mineral carefully and check for light reflecting off of flat surfaces

Physical Properties • 6) Fracture: When a mineral breaks into pieces with uneven surfaces

Physical Properties • 7) Specific gravity: the ratio between the weight of a substance and the weight of the substance in an equal volume of water

Physical Properties • 8) Special Properties: unique properties some minerals have – Examples: Halite- tastes salty • Magnetite- magnets are attracted to it • Calcite- bubbles with HCL (acid test)

B. • Minerals are grouped according to their chemical properties • 1. The elements silicon and oxygen combine to form tetrahedral units

• 2. The physical properties of minerals depend upon the internal arrangement of atoms. • Diamond- Jewelry, Cutting hard surfaces • Graphite- pencil lead, lubricant • Both 100% carbon

• 3. Of the thousands of known minerals, only a few are found almost everywhere

• 4. If you know how to identify about 12 of the most common minerals you will be able to identify minerals in most rocks you are likely to find.

• 5. Nearly all rocks are composed of one or more minerals

• 6. Minerals are the building blocks of most rocks. – Some exceptions include coal.

• Stuff away • Characteristics of a mineral • Physical Properties of a mineral

Igneous rocks • Solidification of molten material (magma) • Named based upon their environment of formation.

Intrusive Igneous Rocks • • AKA. Plutonic Rate of cooling: slow to very slow Size of crystals: 1 mm to more than 10 mm Texture: Coarse/very coarse

Extrusive Igneous Rocks • AKA. Volcanic • Rate of cooling: fast to very fast • Size of crystals: less than 1 mm to noncrystalline • Texture: glassy/fine

Vesicular • Gas bubbles

Felsic

Mafic

Non-crystalline • No visible crystals

Sedimentary Rocks • Deposition, burial, compaction and cementation of sediments

Clastic Sedimentary Rocks • Classified by grain size. • Formed by: deposition, burial, compaction and cementation of sediments • Ex: Siltstone, sandstone, conglomerate, breccia, shale

Crystalline Sedimentary Rocks • Classified by composition • Formed by: compaction and cementation. Crystals from chemical precipitates and evaporates • Ex. Rock salt, gypsum, dolostone

Bioclastic sedimentary rocks • Classified by composition • Formed from: cemented shell fragments and biologic origin • Ex. Limestone • Formed from plant remains • Ex: coal

• 1) Formed in horizontal layers on Earth’s surface because that’s where all of the weathering , erosion and biologic activity takes place

• 2) Fossils are almost exclusively found in sedimentary rocks because formation of the other rock types alters or destroys them. • Igneous melts them • Metamorphic deforms them

• 3) Fossils provide…

Metamorphic Rocks • Formed directly from any type of rock • Extreme heat and pressure cause metamorphism

Changes in Rocks due to Metamorphism • • Recrystallization of unmelted material Density increases Foliation- minerals are aligned Banding- thin layers of alternating minerals

Regional Metamorphism • Occurs when large areas of rock are under intense heat and pressure • Associated with mountain building

Contact Metamorphism • Occurs when molten rock comes in contact with surrounding rock • Heat alters the rock it comes in contact with • Helps to establish relative ages of rocks

Classification of Metamorphic Rocks • Texture- including foliated or banding composition

Degree of metamorphism • Can be a small alteration to major changes depending on the amount of heat and pressure

Parent Material • What the rock used to be before it changed

• • Shale Slate (low) Shale Phyllite (medium) Shale Schist (medium) Shale gneiss (high) • The deeper under ground, the more heat and pressure and the greater the change

The rock cycle • Continuing change from one rock type to another rock type