Properties of Minerals Geologists use characteristics to tell one mineral from another

What is a mineral? S olid N aturally Occuring I Inorganic F ixed Composition C Crystal Form

Groups of Minerals Minerals are grouped by the elements they are made of. Amethyst Beryl (Emerald) Calcite

Mineral Group CharacteristicsExamples Silicates Contain oxygen & silica Contain oxygen & silica The most abundant group of minerals The most abundant group of minerals Quartz, mica MICA Quartz

Mineral Group CharacteristicsExamples Non-Silicates Make up only 5% of the Earth’s crust Make up only 5% of the Earth’s crust Include some of the most important minerals Include some of the most important minerals iron, copper, gold, silver, diamonds, rubies Silver Gold Ruby Iron Copper Diamond

Mineral Group CharacteristicsExamples Carbonates Carbon & oxygen and a positive ion, such as calcium Carbon & oxygen and a positive ion, such as calcium Calcite (CaCO 3 ) Calcite with Duftite inclusions

Mineral Group CharacteristicsExamples Oxides  Metallic ion and oxygen Hematite (Fe 2 )O 3

Mineral Group CharacteristicsExamples Sulfides  Sulfur and a metallic ion Galena (PbS)

Mineral Group CharacteristicsExamples Sulfates   Metallic ion, Sulfur & oxygen Barite (BaSO 4 ) Barite on Calcite BaSo4 / CaCO3 Barite BaSo4

Mineral Group CharacteristicsExamples Native Elements   Single elements Gold (Au), Diamond (C), Silver (Ag)

How do minerals form? 1) Cooling of magma (hot, liquid rock and minerals inside the earth (from the mantle)) –Fast Cooling = No Crystals (mineraloids) –Medium Cooling = small crystals –Slow Cooling = large crystals

How do minerals form? 2) Elements dissolved in liquids (usually water)

Mineral properties Color Luster Habit (Shape) Cleavage & Fracture Streak Hardness Other

Luster: How minerals reflect light Non- metallic Metallic

Physical Properties of Minerals (can be used to identify the mineral) Luster Surface reflection metallic = shiny like metal non-metallic = dull, non-shiny surface Pyrite has a metallic luster Calcite has a non-metallic luster

Pyrite has metallic luster

Quartz has nonmetallic luster

Physical Properties of Minerals (can be used to identify the mineral) Hardness How easily a mineral scratches materials Mohs Hardness Scale Scale from 1 (softest) to 10 (hardest) Test by seeing if the mineral can scratch different objects (like human fingernail, copper, penny, glass, steel file)

Gypsum is soft, it can be scratched by a fingernail.

Calcite is soft, but a little harder because it cannot be scratched by a fingernail, but it can be scratched by a penny.

Fluorite is harder. It can be scratched by a nail, but not a penny or fingernail.

Diamonds are the hardest mineral, so it scratches every mineral.

Mineral Habit (Shape) Shape a mineral takes if grown unimpeded

Physical Properties of Minerals (can be used to identify the mineral) Streak The color of the powdered form of the mineral The color of the streak can be different than the mineral Minerals must be softer than the streak plate

Streak Red chalk on a chalk board makes red marks. White chalk makes white marks. Not all minerals work this way. When some minerals are scratched along a ceramic streak plate, it creates a different color.

Gold When gold is run across a streak plate it makes a yellowish-gold color. That makes sense.

Pyrite or “Fool’s Gold” When pyrite is run across a streak plate, it has a black or dark green streak. Pyrite is not worth much money, while gold is worth a lot. They look alike, so miners call it fool’s gold.

Hematite Hematite’s color is grey, but its streak is red. Hema means blood. The mineral was named hematite because it looked like it was bleeding when it was taken across a streak plate.

Streak…can help identify quartz

Cleavage Not all minerals have cleavage. Some minerals split easily along a flat surface. The number of lines that are created when a mineral is split will be the number of cleavage lines.

Physical Properties of Minerals (can be used to identify the mineral) Cleavage & Fracture –The way the mineral breaks –Cleavage—minerals break along smooth, flat surfaces and every fragment has the same general shape –Fracture—minerals that break at random with rough or jagged edges

Fracture breaks irregularly in all different shapes and sizes. QUARTZ

Physical Properties of Minerals (can be used to identify the mineral) Color Can be misleading Can vary with the type of impurities

Color: Not mineral specific

One mineral property we will use… is COLORHowever...

A mineral can be many different colors. Below is Mica.

Many minerals can be the same color. Below are gold colored minerals. Which one is gold?

The answer… None of them were real gold.

Physical Properties of Minerals (can be used to identify the mineral) Other Properties –Specific gravity (*excellent clue to mineral’s identity) Specific GravitySpecific Gravity –Attraction to magnets –Bending of light –Reaction with hydrochloric acid –Smell & taste (Never taste anything in the our school lab.)

Just like with people… Outside color does not tell you much about the important characteristics.

What is a gem? A Mineral OR Rock that has value Rare ! Sometimes polishing or cutting will add value