LAB 5: Minerals, Rocks & Fossils

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1 Name School LAB 5: s, s & Fossils s are defined as naturally occurring, inorganic, solids with a definite chemical composition and a regular, internal crystalline structure. The keys to this definition are the chemical composition and the crystalline structure. Different chemical compositions result in different minerals. Different crystalline structures, or how the atoms and molecules are arranged, result in different minerals. A good example is diamond and graphite. Both minerals are composed of carbon. The same chemical composition, but two different crystalline structures therefore they are two different minerals. Physical Properties of s The mineral identification process begins with learning about mineral characteristics: which ones to look for, what their definitions are, and which ones are most useful in the identification process. Consistency in chemistry and crystal structure causes a mineral to have consistent physical properties. Physical properties observed from minerals are: Color Luster Hardness Cleavage/fracture Streak Color Although probably the most obvious feature, color is the least diagnostic physical property of most minerals. Color should be recorded, but it should never be used until the end of the identification process. Even then, for most minerals, it is not as important as other properties. For example, although green is a very common color of chlorite specimens, all green specimens are NOT chlorite. Other minerals that can be green include quartz, calcite, augite (pyroxene), hornblende (amphibole), olivine, talc, serpentine, epidote, apatite, and garnet. There are even green feldspars! So record colors that you see, but reserve judgment until you gather all the data and work through the analysis. Luster Luster is a much more important characteristic than color. Luster describes how light is absorbed or reflected by a mineral surface, which affects the mineral s appearance. The two major categories of luster are metallic and nonmetallic. Simply stated, metallic luster is the appearance of a metal, such as steel, chrome, aluminum, or gold. Nonmetallic luster has several varieties glassy (also called vitreous), waxy, resinous, dull, or earthy. Metals are opaque and highly reflective and can be either shiny or dull. Having good light as you make these observations is essential. Patrich Physical Geography Lab 1

2 Hardness Hardness, the resistance of a smooth surface of a mineral to scratching, is a particularly useful physical property in mineral identification. Mohs hardness scale assigns a numerical value of one to ten for ten common minerals. The hardness of an unknown mineral is determined by testing its hardness against known minerals. Cleavage and Fracture Cleavage and fracture describe how a mineral breaks apart. Fracture is an irregular break that does not produce a planar (flat) surface. Although irregular, a fracture surface can have a distinctive appearance. In chrysotile, for example, broken fragments look like splinters while broken surfaces in obsidian may have a conchoidal fracture in which one or more surfaces are smooth and curved like the interior of a seashell. Because cleavage is caused by a certain arrangement of weak bonds in a particular crystalline structure, it can be very characteristic of certain minerals and useful for identification. s can have multiple directions of cleavage, depending upon their crystal structure, and some cleavages can be more perfect than others. Common combinations of cleavage direction are described below. It is important to understand that two parallel cleaved surfaces represent one cleavage direction. Since minerals are 3-dimensional solids, they can have more than one surface, which is broken along the same planar direction. Patrich Physical Geography Lab 2

3 Cleavage Continued: Different Planes of Cleavage Streak Streak is the color of a powdered mineral and is considered to be the true color of a mineral. Different specimens of a mineral may have different colors, but the powdered streak is constant. Dolomite, for example, can be virtually any color imaginable; however, the streak of dolomite is always white. The test for streak is conducted by dragging an edge of the mineral specimen across an unglazed porcelain tile called a streak plate. s powder if their hardness is less than that of the streak plate, which has a hardness of about 7. If a mineral is harder than the streak plate, the mineral scratches the streak plate and you see what appears to be a white streak composed of powdered streak plate. s that are harder than the streak plate are listed on your identification charts with a white streak to help prevent confusion, although their streak is sometimes described as none. Patrich Physical Geography Lab 3

4 Hardness Scale Luster Color Streak Cleavage or Fracture Misc. Properties Name 1 Waxy or Pearly to Light Grey One Perfect Cleavage Slippery Talc Earthy ; Cream; Red- Brown Same as Mass None Used for Aluminum (Box of Chicken Pox) Bauxite 2 Pearly or Vitreous to Colorless One Imperfect or Two Perfect Used =in Drywall Gypsum 2.5 Metallic Silver to Gold Three Cubes Lead Sulfide Galena (Silver) Pyrite (Gold) Vitreous Colorless to Pink Three Perfect Square Salt Halite Vitreous or Pearly Brown to One Perfect Cleavage Elastic; In sheets Biotite Mica Vitreous or Pearly Colorless to One Perfect Cleavage Elastic; In thin sheets Muscavite Mica 3 Earthy ; Blue; Green; Clear Three Rhombohedra Used to Cement Calcite 4 Vitreous Vitreous or Earthy 5 Vitreous Colorless; Green, Purple, etc Light to Dark Blue Yellow; Green; Brown; Blue Four Octahedral None Poor None Massive or Granule or Mammillary Massive or Hexagonal Prisms Fluorite Azurite Apatite Metallic Unless Oxidized Brownish Red Parting Glittery Hematite Vitreous or Pearly 6 Pearly 6.5 Vitreous to Dull 7 Vitreous 7.5 Vitreous Blue to Colorless;. Pink, Etc Grass to Green Colorless;, Pink, Grey; etc Red Brown to Triclimic: Elongated Glittery Kyanite Two Blocky None Orthoclase Conchoidal Jewelry Olivine Conchoidal or Crystalline Monoclinic/ Cross Shaped Jewelry Jewelry Staurolite Patrich Physical Geography Lab 4

5 Activity 1: The Incomplete Mohs Hardness Scale Each group will be provided a box with six unorganized minerals (part of the Mohs Hardness Scale). Using the minerals within the box and this text, please identify each mineral in the box starting left to right. (Top row of box only) 1 Name. 2 Name. 3 Name. 4 Name. 5 Name. 6 Name. The Cycle: Let s Start Putting s Together! Combined with the effects of tectonics, weathering and vegetation, rocks define the natural landscapes we see around us. There are many kinds of rock, and they can be classified in a number of ways. However, geologists classify rocks based on how the rocks were formed. The three classes are igneous rocks (formed directly from liquid rock), metamorphic rocks (formed by direct alteration of existing rocks), and sedimentary rocks (formed by eroded materials from other rocks). Patrich Physical Geography Lab 5

6 Igneous rocks are formed from the solidification of molten rock material. There are two basic types. Intrusive igneous rocks crystallize below Earth's surface and the slow cooling that occurs there allows large crystals to form. Examples of intrusive igneous rocks are diorite, gabbro, granite, pegmatite, and peridotite. Extrusive igneous rocks erupt onto the surface where they cool quickly to form small crystals. Some cool so quickly that they form an amorphous glass. These rocks include andesite, basalt, obsidian, pumice, rhyolite, scoria, and tuff. Color to Grey to Red to Grey to Grey/Pink Peach to Grey to Red ; Grey;. Etc Grey to Green Texture Notes Intrusive or Extrusive Name of Dominant Vesicular E Pumice Glassy Fine Grain Coarse Grain Porphyritic Volcanic Glass Gabbro Basalt Countertop Material Small Structure Porphyritic Bubbles E Porphyritic Granite Tuff E Obsidian E Basalt Augite I Gabbro Augite I E I Granite Rhyolite Scoria Basalt Diorite & Feldspar & Feldspar Pyroxene s Feldspar; ; Hornblende E Andesite Hornblende Patrich Physical Geography Lab 6

7 Sedimentary rocks are formed by the accumulation of sediments. There are three basic types of sedimentary rocks. Clastic sedimentary rocks such as breccia, conglomerate, sandstone, siltstone, and shale are formed from mechanical weathering debris. Chemical sedimentary rocks, such as rock salt, iron ore, chert, flint, some dolomites, and some limestones, form when dissolved materials precipitate from solution. Organic sedimentary rocks such as coal, some dolomites, and some limestones, form from the accumulation of plant or animal debris. Color Red; Grey; etc - Glassy Grey; Red; Red; Brown; ; etc Red; Brown; ; etc to Cream to Yellow Texture Notes Name of Medium- Coarse Banded Flat Pieces Conglomerate Rounded Conglomerate Angular Fine Grained Clastic Clastic Marble Sea Shells Similar Structure to Obsidian 10ft of Debris= 1ft of Coal Compacted Clay Cementation of Broken Fragments Cementation of Broken Fragments Glacial & Highly Weathered Sediments Beaches, Deserts & Deltas Geothermal Sediment Organic Sediment Coquina Chert Coal Shale Conglomerate Breccia Siltstone Sandstone Travertine Limestone Dominant Calcium Carbon Calcium Carbonates Calcite Patrich Physical Geography Lab 7

8 Metamorphic rocks have been modified by heat, pressure and chemical processes, usually while buried deep below Earth's surface. Exposure to these extreme conditions has altered the mineralogy, texture and chemical composition of the rocks. There are two basic types of metamorphic rocks. Foliated metamorphic rocks such as gneiss, phyllite, schist, and slate have a layered or banded appearance that is produced by exposure to heat and directed pressure. Non-foliated metamorphic rocks such as hornfelds, marble, quartzite do not have a layered or banded appearance. Color Texture Notes Name of Dominant Fine Crystals Shiny Between Phyllite & Gneiss Schist Mica ; Pink; Tan; Other Looks like Chewed Bubble Gum ite Sandstone Metallic With Brown Reflection Banded Hard Coal Anthracite Carbon - Granite Banded Foliated- Large Banding Gneiss Feldspar & Diorite Grey; Red; Flat Pieces Once Was Shale Slate, Calcite Pink; ; Grey Nonfoliated. Made of Limestone Marble Calcite Patrich Physical Geography Lab 8

9 Activity 2: & Identification Name School Each group will be provided a box with seven unorganized rocks. Using the previous pages within this lab- Identify whether the sample is Igneous: Intrusive or Extrusive (Ign), Sedimentary (Sed), Metamorphic (Met) or a (Min). Be sure to circle the identifier and then write the full name of the sample. Specimen 7: Ign/Sed/Met/Min Specimen 8: Ign/Sed/Met/Min Specimen 9: Ign/Sed/Met/Min Specimen 10: Ign/Sed/Met/Min Specimen 11: Ign/Sed/Met/Min Specimen 12: Ign/Sed/Met/Min Specimen 13: Ign/Sed/Met/Min Specimen 14: Ign/Sed/Met/Min Specimen 15: Ign/Sed/Met/Min Specimen 16: Ign/Sed/Met/Min Specimen 17: Ign/Sed/Met/Min Specimen 18: Ign/Sed/Met/Min Patrich Physical Geography Lab 9