Presentation on theme: "A mineral is a naturally occurring, inorganic solid that has a crystal structure and a definite chemical composition."— Presentation transcript:
A mineral is a naturally occurring, inorganic solid that has a crystal structure and a definite chemical composition.
Minerals form from Magma * (They form as hot magma cools inside the crust, or as lava hardens on the surface) *Large crystals form when cooling is slow. *Small crystals form when cooling is fast. Minerals form from a hot water solution. *Many minerals form at places where tectonic plates spread apart. When the hot solution hits the cool sea, minerals crystallize and settle to the ocean floor. Minerals form by evaporation *They form when solutions evaporate. *Minerals such as halite formed when ancient seas evaporated.
Minerals are made of atoms. Some minerals are made of only one kind of atoms, such as gold and silver. Most minerals are made of two or more kinds of atoms, such as salt. It is made of sodium and chlorine atoms.
1. Color -Easily observed but few have characteristic color. 2. Hardness -Moh’s hardness scale and scratch test 3. Streak -Color of its powder on unglazed tile 4. Luster -Term used to describe how a mineral reflects light 5. Density -Mass per unit volume 6. Crystal systems - Cubic, hexagonal, tetragonal, orthorhombic, monoclinic, triclinic 7. –Breakage Cleavage and Fracture 8. Special properties (fluorescence, magnetism, scent, react to acid, etc)
Describing a mineral’s color may be easy, but color is not the best way to identify a mineral. Sometimes different atoms get trapped inside a mineral when it forms. These different atoms can change the color of the mineral. These are all images of halite.
Hardness is a better way to describe minerals. There is a scale called the Mohs’ hardness scale The low numbers are soft and the higher numbers are hard. Hard minerals can scratch lower numbers The higher a mineral’s number is, the more minerals it can scratch. The Mohs’ scale is pictured below 1 2 3 4 5 6 7 8 9 10
A tool called a streak plate also helps us to study minerals. A streak plate is made of white tile that can show streak. Different minerals make lines that are different colors. Some lines are the color of the mineral and some are not.
Vitreous Silky Metallic Earthy Luster describes how a mineral appears to reflect light and how brilliant or dull the material is. There are terms used to describe luster. They are: adamantine (brilliant), Metallic (very reflective), submetallic, vitreous (glassy), resinous, silky, pearly, greasy (oily), pitchy, waxy (waxlike), earthy (dull). 70 % of all minerals fit in the vitreous category. This is a test that is based just on visual observations.
This is a useful property to distinguish minerals since they have a specific density. Pure Gold has a density of 19.3 g/cm3.
All minerals have a specific crystal system. Cubic crystals are six sides that meet at right angles, forming a perfect cube
One six fold axis of rotation Hexagon shaped base
3 two-fold axis of rotation 1 two-fold axis of rotation 2 mirror planes
Either one two fold axis of rotation Or one mirror plane Flat, thin sides
Requires either a center Or only translational symmetry
Some minerals break apart in a special way due to their atomic arrangement. Cleavage is a term that means the mineral breaks apart smoothly in flat surfaces. Fracture is a term that means the mineral breaks apart smoothly in more than one direction.
Fluorescence: some minerals have a fluorescent glow under black light. Magnetism: some minerals have Magnetic force. Scent: some minerals have a distinct odor. Reacts to Acid: some minerals have a Reaction to acids.
Many minerals are very expensive and highly valued. How rare a mineral is determines its value. Minerals can be enhanced by dying, oiling, polishing and cutting.