Notes Lab 1 PHYSICAL PROPERTIES OF MINERALS Earth Lab Chapter 2 Crystal Form Crystal Habit the external geometric shape of a crystal which reflects its atomic structure Luster how light is reflected from a fresh surface of a mineral e g metallic sub metallic nonmetallic Hardness the resistance to abrasion on a fresh surface Can it be scratched See MOHS Hardness Scale s 10 index minerals Pg 31 Table 2 3 Earth Lab Talc is 1 and Diamond is 10 The first two minerals Talc and Gypsum can be scratched with a fingernail Minerals harder than 6 are harder than a porcelain streak plate won t streak Streak color of a powdered mineral which is tested by rubbing the mineral across a porcelain streak plate Color hue tint or actual color of a mineral Not generally diagnostic for minerals e g quartz may be colorless milky pink purple smoky etc Cleavage the tendency to break along preferred surfaces called cleavage planes Cleavage planes present flat light reflective surfaces surfaces cut with a rock saw are dull Fracture the tendency to break along an irregular surface May appear hackly rough or conchoidal curved and ribbed Specific Gravity density Note high specific gravity of galena magnetite pyrite Effervescence Acid such as hydrochloric acid HCl applied to CaCO3 causes a fizzing reaction 2H CO3 H2O CO2 fr om HCl from CaCO3 water escaping gas bubbles Magnetic attracted by a magnet Taste unique flavor halite tastes like salt Smell distinctive odor sulfurous smell of galena Feel distinct physical sensation when touched silky talc greasy graphite Double Refraction ray of light splits in two producing two offset images Iceland spar calcite Tenacity resistance to mechanical deformation breaking bending Some examples Brittle describes most minerals copper is ductile can be elongated into wire gold is malleable can be shaped and pounded into a thin leaf Fluorescence short light waves radiate back as long waves changes the color of some minerals Physical properties of minerals Mineralogy Society of America Website http www minsocam org MSA collectors corner id mineral id keyi3 htm Other minerals websites http webmineral com determin shtml http csmres jmu edu geollab Fichter Minerals Minalpha html http pubs usgs gov gip gemstones Notes Lab 2 ROCK FORMING MINERALS Major elements in the Earth s Crust O Si 75 oxygen silica Al Fe Ca Na K Mg aluminum iron calcium sodium potassium magnesium All others 23 Earth Lab Chapter 3 2 100 Rock Cycle the events involving the formation alteration destruction and re formation of the three rock types igneous metamorphic and sedimentary rocks Geologic processes convert each type of rock into the other two types Plate tectonics and climate drive the rock cycle processes The Silicate Ion the basic building block of all silicate mineral structures It is a tetrahedron a pyramidal structure with a central silicon ion si4 surrounded by four oxygen ions O2 giving the formula SiO4 4 Because the silicate ion has a negative charge it often bonds to cations to form electrically neutral minerals The silicate ion typically bonds with cations such as sodium Na potassium K calcium Ca magnesium Mg and iron Fe Chemical Classification Groups of the Rock Forming Minerals 1 Silicates basic chemical building block is the silica tetrahedron SiO4 2 Non Silicates Example a Carbonates Basic unit is CO3 calcite CaCO3 b Sulfates Basic unit is SO4 gypsum CaSO4 2H2O c Sulfides S plus a metal s galena PbS d Oxides O plus a metal s magnetite Fe3O4 e Hydroxides OH plus a metal s limonite FeO OH nH2O f Phosphates Basic unit is PO4 apatite Ca5 PO4 3 F C OH g Halides Halogen ion present halite NaCl h Native elements Occur in elemental form Ag silver Cu copper Au gold Fe iron Pt platinum C graphite diamond S sulfur Feldspars The most abundant group of minerals in the crust They are framework silicates however aluminum has substituted for some of the silicon In addition to silicon oxygen and aluminum the feldspars contain sodium calcium or potassium Feldspars containing potassium are called potassium feldspars or K feldspars Two K feldspars are microcline and orthoclase If sodium or calcium or both are incorporated into the feldspar crystal structure then the mineral is plagioclase feldspar K Orthoclase Microcline Na Plagioclase feldspars Ca A website for the feldspar minerals http www minerals net mineral silicate tecto feldspar feldspar htm Notes Lab 3 IGNEOUS ROCKS Earth Lab Chapter 4 Rock Identification The elements present in the Earth are organized into mineral grains and mineral grains aggregate to form rocks In lab you learned to identify common rock forming minerals by their physical properties now you will learn to recognize common rocks Rocks are mixtures of minerals held together by relatively weak bonds between individual mineral grains or in some cases by cementing materials which act like glue Classification of rocks is based on the way the mineral grains of the rock crystallize Igneous rocks are formed by solidification of magma freezing or by accumulation of fragments ejected during volcanic eruptions Sedimentary rocks are formed by the deposition and subsequent aggregation of rock or mineral fragments produced by erosion and transported by wind or water Some sedimentary rocks form by precipitation of minerals from the dissolved elements present primarily in seawater Metamorphic rocks are formed when existing sedimentary or igneous rocks are subjected to increases in temperature pressure or stress which cause the original mineral grains to recrystallize or be replaced by new minerals stable under the new conditions Igneous Rocks Igneous rocks are composed of hard minerals H 6 mostly silicates Feldspar is the most common igneous mineral Biotite and occasionally muscovite is the only soft mineral Other igneous minerals include quartz hornblende olivine and pyroxene Igneous Rock ID classified by color composition and grain size texture When magma freezes quickly in extrusive volcanic environments crystals grow rapidly from many nuclei resulting in a very fine grained grains too small to see rock When magma cools below the surface intrusive environment heat is lost slowly and fewer nuclei develop so the rock is more coarsegrained COMPOSITION related to color and amount of silica a Felsic light color high amount of silica 70 rich in K feldspar and quartz b Intermediate medium color medium amount of silica 60 c Mafic dark color Fe Mg content equal to silica 50 minerals olivine pyroxene amphibole