jan 27 lecture notes.docx

Minerals & Rocks Olivine (Mg,Fe)2 SiO4 Silicate with abundant Fe and Mg, chemical composition same as that of mantle. Earth?s most abundant mineral Aka peridot, fayalite, forsterite. Occasional gem quality Using mineral properties for identification Atleast 30 distinct properties can be used to identify a mineral Most common: hardness, shape, luster, cleavage, mineral shape, density, acid reaction, color Major mineral groups Silicates ? silicon, oxygen Quartz=one of the more common minerals in the crust (SiO2) Feldspars: most common in silicates common in igneous rocks like granite Carbonates - carbon, oxygen aragonite Sulfates ? sulfur with oxygen Sulfides ? sulfur no oxygen Galena (lead + sulfur) Oxides ? metallic elements + oxygen Rust FeO2 Cuprite (copper exide) Native elements (pure elements) ? copper, silver, gold, platinum, carbon (diamond, graphite) Rocks A solid cohesive aggregate of one or more minerals or mineral materials Rock types Igneous-form from cooling magma Plutonic ? form from magma that cools below the earth?s surface Visible crystals due to slow cooling Volcanic ? form from magma that cool at/above the earth?s surface (eruption) Typically no visible crystals due to rapid cooling Glassy-no crystals-disorganized internal structure due to very rapid cooling (no time to form an atomic structure) Metamorphic-alteration of pre-existing rocks Noted for softness and carving ease Examples: marble, gneiss, schist with garnets These rocks are used for art Sedimentary Clastic- constructed from broken pieces of pre-existing weathered rocks Chemical- precipitated by chemical reactions from water ? via either inorganic or biologically-mediated reactions Inorganic Organic: no visible grains, yet built of shells of microscopic critters that float in the oceans and construct CaCo3 lime shells from Ca, C an O in the water (chalk) Layering characterize many sedimentary rocks Rock properties 1. Mechanical Strength and fracture 2. Hydraulic Porosity: open space within a rock as percentage of the total rock volume Critical property for rocks to enable fluid storage (oil/gas/water) High porosity means lots of open space between pores so that the rock can store fluid Sedimentary rocks have high porosity Igneous rocks have low porosity Permeability: ease with which fluid can travel through a rock Example = Niagara springs ? water emerging from highly permeable lava unit 3. Chemical Example: pouring acid rain on marble will destroy it, which is why we don?t build buildings out of marble