Transcript MINERALS
MINERALS S6E5.b Investigate the composition of rocks in terms of minerals. WHAT IS A MINERAL? • A mineral is a naturally formed, inorganic solid that has a definite crystalline structure. Let’s Break it Down!!! (FRAYER MODEL) • Naturally formed = made in nature/not “man-made”. • Inorganic = non-living • Solid = 3 dimensional, hard • Definite crystalline structure = made of two or more elements; forms crystals. CRYSTALS • Solid, geometric forms of minerals produced by a repeating pattern of atoms or molecules that is present throughout the mineral. How Many Minerals Have Geologists Discovered? • Geologists have discovered over 2,500. • However, we only see about 100 frequently. • Less than 20 are widely distributed. • 98.5% of the Earth consists of just eight elements. 8 Elements of the Earth 1) 2) 3) 4) 5) 6) 7) 8) Oxygen (46.6%) Silicon (27.7%) Aluminum (8.1%) Iron (5%) Calcium (3.6%) Sodium (2.8%) Potassium (2.6%) Magnesium (2.1%) Most Common Rock-Forming Minerals Quartz (SiO2) Calcite (CaCO3) Augite (Ca, Na) Hematite (Fe2O3) Micas Feldspars NATIVE ELEMENTS • A mineral that is composed of only one element. • Ex: gold & silver SILICATES vs. NONSILICATES • Minerals divided into 2 groups based on chemical composition • Minerals that contain a combination of silicon & oxygen are silicate minerals. • Silicate minerals make up more than 90% of the Earth’s crust. SILICATES vs. NONSILICATES • Minerals that do not contain a combination of silicon & oxygen are nonsilicate minerals. • Classes: native elements, carbonates, halides, oxides, sulfates, & sulfides. IDENTIFYING MINERALS • Color • Luster • Streak • Cleavage & Fracture • Hardness • Density • Special Properties COLOR • • • • What you see on the ouside! Not the best way to identify a mineral Same mineral can come in a variety of colors Ex: Quartz---purest state is clear; impurities can cause it to be different colors • Exposure to air & water can change color (Ex: pyrite---usually golden but changes to brown or black when exposed to air & water) LUSTER • Luster: the way a surface reflects light; whether a mineral is shiny or dull! • Metallic, submetallic or nonmetallic luster • Shiny = metallic luster • Reflective/dull = submetallic • Dull= nonmetallic luster STREAK • Streak: color of a mineral in powdered form • Rub mineral against a piece of unglazed porcelain (streak plate) • Mark left on streak plate is the streak. • Color of streak not always the color of the mineral sample. • Not affected by air or water • More reliable than color in identifying a mineral CLEAVAGE & FRACTURE • How a mineral breaks • Determined by arrangement of atoms • Cleavage: tendency to break along smooth, flat surfaces (Ex: halite & mica) • Fracture: tendency to break unevenly along curved or irregular surfaces (Ex: quartz) HARDNESS • Mineral’s resistance to being scratched • Mohs Hardness Scale • Ranges from 1 to 10; 1 being softest (talc) & 10 being the hardest (diamond) • Scratch tests; scientists use common items to test hardness. – – – – Fingernail has a hardness of 2-2.5 Knife blade is 3-4 Glass is 5-6 Steel file or nail is 6.5-7 A mineral of a given hardness will scratch any mineral that is softer than it is. DENSITY • The measure of how much matter is in a given amount of space. • Density is a ratio of an object’s mass to its volume • D=m/v • Measured in grams per cubic centimeter (g/cm3) DENSITY • Water has a density of 1g/cm3 • Used as a reference point for other substances. • Object sinks---it’s density is greater than 1g/cm3 • Object floats---it’s density is less than 1g/cm3 SPECIAL PROPERTIES • Some properties are particular to only a few types of minerals • Fluorescence, chemical reaction, optical properties, magnetism, taste, radioactivity