Atoms • Atoms – basic building blocks for all earth materials; consist of 3 basic components: protons, neutrons, electrons
Atoms combine to form Elements • Elements– fundamental component that can not be broken down into other substances by ordinary chemical processes • Elements combine to form minerals
Do you Know?
General Facts About Minerals Around 4,000 minerals have been identified • A few are “native elements” -- made of only one element, such as sulfur, gold. copper, and graphite (carbon) • Most are compounds, especially the silicate group (Si, O). • Other important groups are oxides, carbonates, and sulfides.
MINERALS NATIVE ELEMENTS Gold (Au) Silver (Ag) Platinum (Pt) Diamond (C) Graphite (C) Sulfur (S) Copper (Cu) Gold Copper Silver
Of the almost 4000 known minerals, only about 30 are common. The most common are quartz, feldspar, mica, and calcite.
These minerals make up most of the rocks found in the Earth’s crust.
In fact, over 60% of the Earth’s crust is made up of the family of minerals known as feldspar!
To be able to identify these and other minerals, we need to look at the properties used to separate and distinguish these minerals.
Identifying Minerals Remember!: Rarely is a mineral identified by a single property. These properties need to be considered together to correctly identify a mineral.
color Color is the most easily observed mineral property and the least useful!
color Some exceptions to the color rule would be cinnabar, which is always red, and malachite, which is green.
color Many minerals have a similar color.
color Many minerals can turn colors due to impurities, or they can change colors in various circumstances.
color For example, pure quartz is colorless or white, impurities can make the mineral rose, purple or pink!
Discuss the following! How many of the characteristics of minerals can you name? Why isn’t color a very good property to identify most minerals?
luster Luster refers to the way a mineral shines in reflected light. Notice the difference between these two minerals?
luster The mineral on the left has a metallic luster, the one on the right, a nonmetallic luster.
luster There are several terms used to describe nonmetallic luster. Examples could be vitreous, like the quartz on the left, or pearly, like the gypsum on the right.
Other terms that might be used include greasy, dull, and earthy. Can you tell which of these has an earthy luster and which has a vitreous luster? Were you Right? Vitreous Earthy
streak Streak of a mineral is the color of its powder when rubbed on an unglazed white tile.
streak The streak is often not the same color as the mineral. A minerals color may vary, but the streak rarely will!
cleavage The cleavage of a mineral is its tendency to split easily or to separate along flat surfaces. Cleavage can even be observed on tiny mineral grains making it a very useful property!
cleavage Mica is probably the best example as it splits into thin sheets. It is said to have one perfect cleavage.
cleavage Feldspar splits readily in two directions, always at or near right angles.
cleavage Calcite and galena cleave in three directions. They are said to have three good cleavages.
cleavage Not all minerals show cleavage. Those that don’t break along cleavage surfaces are said to have fracture.
Identifythemineralsbelowforcleavageandfracture CLEAVAGE FRACTURE in
Discuss the following! There are four common minerals, how many can you name? Of the four common minerals, which one makes up over 60% of the Earth’s crust?
Hardness The hardness of a mineral is its resistance to being scratched. Diamond is the hardest of all minerals, and talc is the softest.
Hardness Friedrich Mohs devised a hardness scale. In this scale, ten wellknown minerals are given numbers from one to ten. Lets take a look at the ten minerals used and some of the simple tests.
Hardness Talc (left) is the softest and has a hardness of 1. A soft pencil lead will scratch talc. Gypsum is a bit harder and has a hardness of 2. A fingernail scratches gypsum.
Hardness Calcite (left) has a hardness of 3 and a copper penny just scratches it. Fluorite has a hardness of 4 and it can be scratched by an iron or brass nail.
Hardness Apatite (left) has a hardness of 5 and can be scratched by a steel knife blade. Feldspar has a hardness of 6 and it will scratch a window glass.
Hardness Quartz (left), with a hardness of 7, is the hardest of the common minerals. It easily scratches hard glass and steel. Topaz has a hardness of 8 and will scratch quartz.
Hardness Corundum (left) has a hardness of 9. Corundum will scratch topaz. Diamond with its hardness of 10 can easily scratch the rest of the minerals.
Absolute Hardness1 Talc72 Orthoclase3 Gypsum100 Quartz9 Calcite200 Topaz21 Fluorite400 Corundum48 Apatite1600 Diamond
Discuss the following! Does this mineral show cleavage or fracture? Of the four most common minerals, which is the highest hardness?