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Elements and Compounds in their solid form make up… What is a Mineral? A Mineral is a naturally occurring Inorganic Solid with a definite chemical composition and a crystalline structure. That means that… •It can’t be organic in origin •It can’t be a liquid and.. •It has to have a crystal structure 5 Requirements 1. Mineral are naturally occurring substances. 2. Minerals are solids. 3. Minerals have a definite chemical composition (i.e. they are elements or compounds, NOT mixtures). 4. The atoms that make up minerals are arranged in an orderly pattern (They form crystals). 5. Minerals are inorganic. (They were never alive.) (Some scientists do classify a few substances as organic minerals, but that is going outside the accepted definition.) How many different minerals are there on Earth??? Answer:About 4,000 Silicon and Oxygen are the two most abundant elements in Earth’s crust. Oxygen makes up about 47% by mass of the Earth’s crust and Silicon is about 28%. Composition of the Earth’s Crust Eight Elements that make up over 98% of Earth’s Crust -Oxygen (O) -Silicon (Si) -Aluminum (Al) -Iron (Fe) -Calcium (Ca) -Sodium (Na) -Potassium (K) -Magnesium (Mg) Minerals • Minerals may be subdivided into two majors groups: – SILICATES – NON-SILICATES Minerals • Silicates are by far the most abundant mineral group accounting for more than 90% of the Earth's crust. Silicates are the major rock-forming minerals. It follows that oxygen and silicon are the most abundant elements in the crust. Minerals • The basic building block of the silicates is the silica tetrahedron. Each silicon atom is attached to four oxygen atoms by tetahedral bonds. This results in a -4 charge on the SiO4-4 group. And….. The percent composition of Silicate Minerals in an igneous rock determine a lot of the characteristics of that rock and the magma that formed it. Minerals There are many ways in which the SiO4 tetrahedra can be assembled to build neutral silicate mineral structures. These structures are the major rock-forming minerals. • Isolated tetrahedra balanced by the cations magnesium (Mg), iron (Fe),calcium (Ca) – – Olivine (Mg, Fe)2SiO4, Magnesium Iron Silicate and Garnet Minerals The typical pyroxene structure contains chains of SiO3 tetrahedrons • The slope of the tetrahedral pyramids helps to determine the cleavage angle of the pyroxenes at nearly 90o degrees (actually 93o and 87o). Minerals Common amphiboles include: • Actinolite Ca2(Mg, Fe+2)5 Si8O22(OH)2 • Anthophyllite (Mg, Fe)7 Si8O22(OH)2 • Arfvedsonite Na3(Fe+2)4Fe+3 Si8O22(OH)2 • Cummingtonite Mg7 Si8O22(OH)2 • Edenite NaCa2Mg5 Si8O22(OH)2 • Fluorrichterite Na(CaNa)Mg5 Si8O22F2 • Glaucophane Na2(Mg3Al2) Si8O22(OH)2 • The Hornblende Series Ca2(Mg, Fe+2)4 (Al, Fe+3)Si7AlO22(OH)2 • Double chains of tetrahedra balanced by similar cations. Minerals • • • Micas and Clay Minerals Sheets of tetrahedra are the building blocks. Aluminum is also involved in these sheet structures which are charge-balanced by the cations Mg, Na and K. Most common mica minerals: muscovite, biotite Minerals • • • • • Feldspars A second group of aluminosilicates. Tetrahedra form threedimensional frameworks with Ca, Na and K as the balancing cations. They are very abundant. Feldspars are subdivided into K-Na bearing alkali feldspars and the Ca-Na solid-solution series called the plagioclase feldspars. The K-feldspars or alkali felspars: •Microcline, (Potassium aluminum silicate) •Sanidine, (Potassium sodium aluminum silicate) •Orthoclase, (Potassium aluminum silicate) Minerals • • • • • Feldspars A second group of aluminosilicates. Tetrahedra form threedimensional frameworks with Ca, Na and K as the balancing cations. They are very abundant. Feldspars are subdivided into K-Na bearing alkali feldspars and the Ca-Na solid-solution series called the plagioclase feldspars. The plagioclase feldspars: •Albite, (Sodium aluminum silicate) •Oligoclase, (Sodium calcium aluminum silicate) •Andesine, (Sodium calcium aluminum silicate) •Labradorite, (Calcium sodium aluminum silicate) •Bytownite, (Calcium sodium aluminum silicate) •Anorthite, (Calcium aluminum silicate) Minerals • • Quartz Silica tetrahedra alone can form a neutral threedimensional framework structure with no need for other cations. This arrangement forms a very stable structure Popular as ornamental stone and as gemstones •Amethyst is the purple gemstone variety. •Citrine is a yellow to orange gemstone variety that is rare in nature but is often created by heating Amethyst. •Milky Quartz is the cloudy white variety. •Rock crystal is the clear variety that is also used as a gemstone. •Rose quartz is a pink to reddish pink variety. •Smoky quartz is the brown to gray variety. Minerals • • Quartz SiO2 Silica tetrahedra alone can form a neutral threedimensional framework structure with no need for other cations. This arrangement forms a very stable structure Popular as ornamental stone and as gemstones •Amethyst is the purple gemstone variety. •Citrine is a yellow to orange gemstone variety that is rare in nature but is often created by heating Amethyst. •Milky Quartz is the cloudy white variety. •Rock crystal is the clear variety that is also used as a gemstone. •Rose quartz is a pink to reddish pink variety. •Smoky quartz is the brown to gray variety. Minerals • • Quartz Silica tetrahedra alone can form a neutral threedimensional framework structure with no need for other cations. This arrangement forms a very stable structure Popular as ornamental stone and as gemstones •Amethyst is the purple gemstone variety. •Citrine is a yellow to orange gemstone variety that is rare in nature but is often created by heating Amethyst. •Milky Quartz is the cloudy white variety. •Rock crystal is the clear variety that is also used as a gemstone. •Rose quartz is a pink to reddish pink variety. •Smoky quartz is the brown to gray variety. Minerals • • Quartz Silica tetrahedra alone can form a neutral threedimensional framework structure with no need for other cations. This arrangement forms a very stable structure popular as ornamental stone and as gemstones •Amethyst is the purple gemstone variety. •Citrine is a yellow to orange gemstone variety that is rare in nature but is often created by heating Amethyst. •Milky Quartz is the cloudy white variety. •Rock crystal is the clear variety that is also used as a gemstone. •Rose quartz is a pink to reddish pink variety. •Smoky quartz is the brown to gray variety. Minerals There are a few important groups of non-silicate minerals. Only the carbonates are significant as rock-forming minerals. The remaining mineral groups are often ore minerals and provide economic sources for various elements. The important non-silicate groups are: – – – – – Carbonates Halides Oxides and Hydroxides Sulfides (and Sulfates) Phosphates Minerals Non-silicates: • • • • • • • • • • • Carbonates: CO3 The important carbonates are the minerals calcite and dolomite. Both are significant rock-forming minerals. The Calcite Group: Calcite (Calcium Carbonate) Gaspeite (Nickel Magnesium Iron Carbonate) Magnesite (Magnesium Carbonate) Otavite (Cadmium Carbonate) Rhodochrosite (Manganese Carbonate) Siderite (Iron Carbonate) Smithsonite (Zinc Carbonate) Sphaerocobaltite (Cobalt Carbonate) Minerals Non-silicates: • Evaporite: A mineral or substance that forms as a precipitate (solid) as water it was dissolved in evaporates. Halides including the minerals halite, sylvite and fluorite; Sulfates including the minerals gypsum and anhydrite. The most famous halide mineral, halite (NaCl) or rock salt Minerals Non-silicates: • Evaporite: A mineral or substance that forms as a precipitate (solid) as water it was dissolved in evaporates. Halides including the minerals halite, sylvite and fluorite; Sulfates including the minerals gypsum and anhydrite. •Fluorite: CaF2, Calcium Fluoride Minerals Non-silicates: • Evaporite: A mineral or substance that forms as a precipitate (solid) as water it was dissolved in evaporates. Halides including the minerals halite, sylvite and fluorite; Sulfates including the minerals gypsum and anhydrite. •Gypsum:CaSO4-2(H2O), Hydrated Calcium Sulfate Minerals Non-silicates: • • • • • • Oxides and Hydroxides Oxides include minerals like hematite (Fe2O3) and magnetite (Fe3O4) Hydroxides include minerals like limonite (actually a mixture of iron (III) oxides and hydroxides) and goethite (FeO(OH)). Important minor constituents in rocks. Aluminum oxide bauxite can also occur as a rock-forming mineral. Oxide minerals are exploited as economic sources of many elements including aluminum, antimony, iron, manganese, tin, and uranium. Minerals Non-silicates: • • Oxides Oxides (hematite and magnetite) Fe2O3, Iron Oxide • • • • Hydroxides (limonite and goethite) Important minor constituents in rocks. Aluminum oxide bauxite can also occur as a rock-forming mineral. Oxide minerals are exploited as economic sources of many elements including aluminum, antimony, iron, manganese, tin, and uranium. Minerals Non-silicates: • • Oxides Oxides (hematite and magnetite) Fe3O4, Iron Oxide • • • • Hydroxides (limonite and goethite) Important minor constituents in rocks. Aluminum oxide bauxite can also occur as a rock-forming mineral. Oxide minerals are exploited as economic sources of many elements including aluminum, antimony, iron, manganese, tin, and uranium. Minerals Non-silicates: • • • • Sulfides The mineral pyrite is the only sulfide that occurs commonly in rocks. Sulfides are most important as economic minerals providing the main sources of elements such as arsenic, copper, lead, nickel, mercury, molybdenum and zinc. FeS2, Iron Sulfide Minerals Non-silicates: • • • • Sulfides The mineral pyrite is the only sulfide that occurs commonly in rocks. Sulfides are most important as economic minerals providing the main sources of elements such as arsenic, copper, lead, nickel, mercury, molybdenum and zinc. PbS, Lead Sulfide, Galena Minerals Non-silicates: • • • • Sulfides The mineral pyrite is the only sulfide that occurs commonly in rocks. Sulfides are most important as economic minerals providing the main sources of elements such as arsenic, copper, lead, nickel, mercury, molybdenum and zinc. CuFeS2, Copper Iron Sulfide, Chalcopyrite Minerals Non-silicates: • • Phosphates are relatively rare. The only important phosphate mineral is apatite. Ca2Fe(PO4)2 · 4H2O, Hydrated Calcium Iron Phosphate A Bit More on Silicates High Silica content forms lightcolored rocks. While lower (but only by about 25%) Silica content forms darker-colored rocks. How do Minerals Form??? 1. Minerals form in cooling magma chambers - usually combining into igneous rocks like granite. Different types of minerals crystallize at different temperatures Decreasing temperature Bowen’s Reaction Series Mineral formation in a Magma Chamber Some Common Minerals and Rocks that Form from Cooling and Crystallizing Magma Olivine Pyroxene Peridotite - Mostly Olivine Gabbro- Pyroxene and Olivine Andesite- Hornblend and Biotite and Plagioclase Feldspar Potassium Feldspar Pink Granite Mineral Fractionalization in a Magma Chamber 2. Metamorphic Minerals: Some minerals occur as the result of Recrystallization and Reaction within existing rocks which produces new minerals in response to changes in and 3. Some types of minerals form as water containing dissolved ions slowly evaporates (i.e. evaporites that precipitate out). Salt deposits 4. Hydrothermal Solutions • The last way that minerals can form is when hot water solutions containing dissolved substances (i.e. hydrothermal solutions) come into contact with existing minerals. • This contact can lead to chemical reactions that form new minerals. • Also, when these solutions cool some of the elements in them combine to form minerals like quartz and pyrite. Quartz How long does it take for minerals to form? • Minerals in solution in water can form relatively quickly when the water evaporates. • Minerals in magma can form as quickly as the magma/lava can crystallize (lava can cool in minutes, while magma can take thousands of years). A Crystal is…. A regular geometric solid with smooth surfaces called…. The orderly arrangement of ions, molecules, or atoms, in any mineral determines the shape of its crystals. Although there are thousands of different types of minerals, their crystals come in six basic types of shapes CRYSTAL HABIT • The crystal habit of a mineral describes its visible external shape. It can apply to an individual crystal or an assembly of crystals. • Each crystal can be described by how well it is formed, ranging from euhedral (perfect to near-perfect), to subhedral (moderately formed), and anhedral (poorly formed to no discernable habit seen). Habit Image Description Common Example(s) Acicular Needle-like, slender and/or tapered Natrolite, Rutile Amygdaloidal Almond-shaped Heulandite, subhedral Zircon Bladed Blade-like, slender and flattened Actinolite, Kyanite Botryoidal or globular Grape-like, hemispherical masses Hematite, Pyrite, Malachite, Smithsonite, Hemimorphite, Adamite, Variscite Habit Columnar Coxcomb Image Description Similar to fibrous: Long, slender prisms often with parallel growth Aggregated flaky or tabular crystals closely spaced. Common Example(s) Calcite, Gypsum/ Selenite Barite, Marcasite Pyrite, Galena, Halite Cubic Cube shape Dendritic or arborescent Pyrolusite and Tree-like, other Mn-oxide branching in one minerals, or more direction Magnesite, from central point. native copper Habit Dodecahedral Image Description Common Examples Dodecahedron, 12-sided Garnet Drusy or encrustation Aggregate of minute crystals coating a surface or cavity Uvarovite, Malachite, Azu rite Enantiomorphic Mirror-image habit (i.e. crystal twinning) and optical characteristics; right- and left-handed crystals Quartz, Plagioclase, Staurolite Equant, stout Length, width, and breadth roughly equal Olivine, Garnet Extremely slender prisms Serpentine group, Tremolite (i.e. Asb estos) Fibrous Crystal Habit • There are many more additional habits to ones listed here. • Also remember that these habits do not always form well – in many cases they are distorted and in some cases they are are indistinguishable. Only 30 of the 4,000 known minerals are common. These 30 minerals are known as the rock-forming minerals Most rock-forming minerals are… The percent composition of Silicate minerals in a rock determines the type of rock it is. Rocks are often made of several different minerals. Rocks that have a high percentage of Silicates are light in color, and are called Felsic rocks. Rocks that have a low percentage of Silicates are dark in color, and are called Mafic rocks. Minerals are identified and classified by visual inspection, and by performing simple tests to determine their physical, and sometimes their chemical, properties. Color is the most easily observed, but least reliable property of a mineral for identification. This is because the color of many minerals varies with the kind of impurities in the mineral. Luster is the way in which a mineral shines in the light. Streak is the color of the powder left on a streak plate when a mineral is rubbed on it. Streak is much more reliable than color because, although the color of a mineral changes, its streak does not. Cleavage is the tendency of a mineral to split in a particular direction. “Sheety” Cleavage Feldspars always cleave readily at or near right angles. Fracture is the tendency of a mineral to break in directions other than along crystal faces or cleavage surfaces. Conchoidal or shell-like fracture Fibrous fracture Hardness is the resistance of a mineral to being scratched. The Mohs Hardness Scale is one of the most effective tool for identifying minerals. Additional Properties Some other properties can also give us clues about identity: • Magnetism (Magnetite) • Glowing under ultraviolet light (Fluorite) Magnetite • Salty taste (Halite) • Smell (Sulfur) • Reaction to HCl (Calcite)