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.

MINERAL STRUCTURE To understand “crystalline structure”, you need to know a little about the elements that make up a mineral.

MINERAL STRUCTURE Elements: pure substances that cannot be broken down into simpler substances by ordinary chemical means. All minerals contain 1 or more of the 92 naturally occurring elements.

MINERAL STRUCTURE Each element is made of only 1 kind of atom. Atom: smallest part of an element w/all of the properties of that element. Minerals are made up of atoms of one or more elements.

MINERAL STRUCTURE Most minerals are made of compounds of several different elements. Compound: a substance made of two or more elements that have been chemically joined or bonded. Ex: NaCl (halite)

MINERAL STRUCTURE Native elements: a mineral that is composed of only one element. Ex: gold & silver

MINERAL STRUCTURE Crystals: solid, geometric forms of minerals produced by a repeating pattern of atoms or molecules that is present throughout the mineral.

MINERAL STRUCTURE Each mineral has a definite crystalline structure.

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 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 Shiny or dull = luster Metallic, submetallic or nonmetallic luster Shiny = metallic luster Dull= submetallic or 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 & 10 being the hardest 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/cm 3 )

DENSITY Water has a density of 1g/cm 3 Used as a reference point for other substances. Object sinks---it’s density is greater than 1g/cm 3 Object floats---it’s density is less than 1g/cm 3

DENSITY Ratio of an object’s density to the density of water is called the object’s specific gravity. Ex: specific gravity of gold is 19. That means gold has a density of 19 g/cm 3. 1 cm 3 of gold contains 19 times as much matter than 1 cm 3 of water contains.

SPECIAL PROPERTIES Some properties are particular to only a few types of minerals Fluorescence, chemical reaction, optical properties, magnetism, taste, radioactivity