Geology Lecture Notes Minerals & Rocks Minerals are the building blocks of rocks. Mostly minerals are combinations of elements Native elements do not need to combine with other elements to create minerals like most minerals do. Gold Copper Silver Carbon Sulfur are native elements which can be their own mineral. Definition of a Mineral: Naturally occurring Solid Definite Chemical Composition Ordered Atomic Arrangement Inorganic Crystalline Structure- Atoms in a mineral are specifically ordered. A solid with disordered atoms is called a glass. Polymorphs- Minerals with the same composition but different structure. Crystals grow as atoms attach to mineral surfaces. Growth starts from a central seed crystal. Growth expands outward as atoms accumulate. Crystals grown by solidification from a melt, precipitation from solution, or solid-state diffusion. Way to identify Minerals: 1. Crystal Form- The form which the crystal has taken after growth or during growth. 2. Crystal Habit- A description of the minerals shape. The ideal shape of crystal faces. 3. Luster- The way the light goes into the rock and the was the surface scatters the light. Can be metallic (looks like a metal) or nonmetallic. 4. Color- Not a great indicator for minerals yet can be a good indicator for some minerals. 5. Streak- A diagnostic property. The color crushed on an unglazed porcelain plate. Congruent streak (streak color the same as the mineral) or Incongruent streak (streak color differs from the minerals). 6. Hardness- Mohs Hardness Scale. Shows you can describe all minerals on this 10-point scale depending on which mineral can scratch the other. Memorize the 10 minerals on Mohs Hardness Scale!!! 7. Cleavage- The tendency to break along planes of lattice weakness. Cleavage produces flat shiny surfaces. Described by the number of planes and their angles. 1,2,3,4 and 6 cleavages are possible. 8. Fracture 9. Specific Gravity- The number of times denser a mineral is compared to water. Density= Mass/Volume More Ways of Identifying 1. Taste 2. Smell 3. Feel 4. Elasticity 5. Magnetism 6. Effervescence 7. Diaphaneity- Surface Transparency 8. Piezoelectricity 9. Pyroelectricity 10. Refractive Index- Most important way of identifying a mineral 11. Malleability 12. Ductility 13. Sectility- Cut with a knife? 74.3% of Crustal Minerals consist of Silicate. Silicon and Oxygen. Amphibole Group- Two perfect cleavages; elongated crystals. Pyroxene Group- Single chain structures bonded together by Iron and Magnessium. They are a black to green color, they have 2 distinctive cleavages at 90 degrees, and stubby crystals. Augite is the most common pyroxene. Feldspar Group- All four oxygen?s in the silica tetrahedral are shared. Also contains the Silica (Quartz) group which only contains only silicon and oxygen. Mica Group- Characterized by one direction of perfect cleavage. Biotite- Dark Muscovite- Light Look at and study slide 28 of Monday Sept, 14th slide show Important Rock Forming Minerals (On quiz memorize) Quartz Feldspar (Orthoclase and Plagioclase Mica (Muscovite-white, Bitotite-black) Rocks are coherent, naturally occurring aggregates of minerals Three types of rocks Igneous-Frozen from magma Sedimentary- Clastic or precipitated Metamorphic- Modified by pressure and temperature Clastic- rocks cemented together most of earth?s surface Crystalline- Interlocking crystals bulk of the earth Porfory- Fossils are found only in sedimentary rocks! The Rock Cycle It starts as magma, then it freezes to form an igneous rock, erode and transport the igneous rock creates sediments, bury and wait hundreds of years so create the sedimentary rock, the sedimentary rock undergoes heat and pressure which turns the rock into a metamorphic rock and then if the metamorphic goes even deeper it melts again turning back into magma. Although this is the basic cycle there are many short cuts to go from one type of rock to another. Igneous rocks Solidifies from 1,100 degrees- 650 degrees C. The temperature that it takes to solidify the rock varies depending on the rocks composition. Earth is mostly igneous rock consisting of magma and lava. The stuff underground is magma and when it comes up to the surface through a volcano it is classified as lava. Classification of Igneous Rocks Mineral content. Does it have Quartz in it or Olivine? Fine grained or coarse-grained texture? Partial melting- removes silica rich materials first (quartz) and leaves high temperature minerals behind (olivine). It separates magma. Changing the materials that arrive to the earths surface. Assimilated rock The order in which crystals form in the magma chamber Olivine 1st Pyroxene 2nd Amphibole 3rd Biotite 4th Quartz 5th Look at terms on first slide of 9/21 lecture and memorize for testing material
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