Mineral - A naturally occurring, inorganic, homogeneous solid with a definite chemical composition and an ordered atomic arrangement. naturally occurring - materials synthesized in laboratory do not count, must be formed by natural processes in wild inorganic - not formed by organic chemistry (e.g., sugars, etc.) homogeneous solid - single substance in solid phase which cannot be physically separated into simpler compounds definite chemical composition - composition can be represented as chemical formula (e.g., NaCl), although variation in exact composition is possible (e.g., (Mg, Fe)2SiO4 ) [range in color, hardness, specific gravity] ordered atomic arrangement – repeating structure at the atomic level, which expresses as symmetry in large specimens, i.e., crystalline structure. http://www.uoregon.edu/~jrice/geol311 Mineral Properties • • • • Crystal Form Cleavage/Fracture Color Streak Color Luster • • • • • Hardness Tenacity Specific Gravity Acid Test Magnetism Crystal symmetry is controlled by the atomic structure of mineral Mineral Properties • Crystal Form • Cleavage/Fracture Color • Streak Color • Luster • • • • • Hardness Tenacity Specific Gravity Acid Test Magnetism Characteristic for some minerals, useless for most Quartz Jasper Citrine Rose Quartz Quartz SiO2 Amethyst Hardness = 7 Carnelian Onyx Smokey Quartz Mineral Properties • Crystal Form • Cleavage/Fracture • Color Streak Color • Luster • • • • • Hardness Tenacity Specific Gravity Acid Test Magnetism Streak Color - Color of powdered mineral, which may or may not be the color of the crystal hematite streak color Mineral Properties • • • • • Crystal Form Cleavage/Fracture Color Streak Luster • Hardness • Tenacity Specific Gravity • Acid Test • Magnetism Specific Gravity - density of the material (g/cm3) Specific Gravity Related to both the atomic weight of the contained elements, and how tightly the atoms are packed Orthorhombic Carbonates All minerals have same structure, only cation differs Mineral Formula Cation g/cm3 Aragonite CaCO3 20 2.95 Strontianite SrCO3 38 3.76 Witherite BaCO3 56 4.29 Cerrusite PbCO3 82 6.55 See Page 82 in Lab Manual for Specific Gravities of some minerals Mineral Properties • • • • Crystal Form Cleavage/Fracture Color Streak Color Luster • • • • • Hardness Tenacity Specific Gravity Acid Test Magnetism Luster - quality of light reflected from mineral surface Luster - quality of light reflected from mineral surface pyrite metallic gold silver Luster quality of light reflected from mineral surface non-metallic Some minerals may be listed in both metallic and non-metallic, or in the incorrect table, i.e., limonite pearly vitreous (glassy) resinous Mineral Properties • • • • • Crystal Form Cleavage/Fracture Color Streak Color Luster • • • • Hardness Tenacity Specific Gravity Acid Test Magnetism Hardness - resistance of mineral to scratching or abrasion Mohs Hardness Scale Austrian mineralogist F. Mohs, 1824 hard Higher numbered minerals Based on relative scratch lower numbered minerals hardness of 10 common minerals 10. Diamond C 9. Corundum Al2O3 8. Topaz Al2SiO4(F,OH)2 7. Quartz SiO2 6. Orthoclase KAlSi3O8 glass plate 5. Apatite Ca5(PO4)3(F,Cl,OH) 4. Fluorite CaF2 copper penny 3. Calcite CaCO3 fingernail 2. Gypsum CaSO4 soft 1. Talc Mg3Si4O10(OH)2 Muscovite Hardness < 2 Can scratch with fingernail (H=2.5) Fig. 02.14 Fluorite Hardness =4 Fig. 02.15c Can scratch copper penny (H=3.5), but not glass plate (H=5.5) Quartz Hardness =7 Fig. 02.15a Scratches glass plate (H=5.5). Hardest of common minerals Mineral Properties • • • • • Crystal Form Cleavage/Fracture Color Streak Luster • Hardness • Tenacity • Specific Gravity Acid Test • Magnetism Reaction to dilute acid; especially useful in identifying carbonate minerals Minerals like calcite react with weak acid, dissolving the mineral and producing lots of bubbles (effervescence) Calcite: CaCO3 HCl + CaCO3 > H2O + Cl- + Ca+ + CO2 Dolomite: CaMg(CO3)2 Mineral Properties • • • • • Crystal Form Cleavage/Fracture Color Streak Luster • • • • Hardness Tenacity Specific Gravity Acid Test Magnetism Some minerals strongly attract magnets. Characteristic of magnetite and some other iron minerals Mineral Properties • Crystal Form Cleavage/Fracture • Color • Streak Color • Luster • • • • • Hardness Tenacity Specific Gravity Acid Test Magnetism Fracture - any breakage that is not cleavage conchoidal fracture Characteristic of quartz, chert and flint conchoidal fracture Fig. 02.23 Mineral Properties • Crystal Form Cleavage/Fracture • Color • Streak Color • Luster • • • • • Hardness Tenacity Specific Gravity Acid Test Magnetism Cleavage - tendency to split along planes of weakness corresponding to weaker chemical links in internal structure of crystal A single crystal can display several cleavage directions. 1 direction 2 directions The cleavage directions are not always at right angles to each other. They also are not necessarily parallel to the crystal faces of the mineral. One Direction of Cleavage Fig. 02.19a One Direction of Cleavage Cleavage Direction Each set of parallel planes of weakness is one direction Two Directions of Cleavage Three Directions of Cleavage Fig. 02.22 http://www.geology.sdsu.edu/visualgeology Four Directions of Cleavage Fluorite Crystals http://www.xpsdata.com/ http://www.greatsouth.net/ Six directions of Cleavage: Sphalerite (ZnS)