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Garnet (Almandine)
Streak: white
Hardness: 7 – 7.5
Chemical Formula: Fe3Al2(SiO4)3
Garnets are a group of silicate minerals. Almandine is the most common of the garnet group and always features a red color.
Crystals of almandine often have well-developed faces and complex crystalline structures. Due to its color, almandine garnets are frequently cut and used as gemstones, but coarse varieties are often crushed for use as an abrasive.
Photo: Almandine by Rock Currier is licensed under the Creative Commons Attribution 3.0 Unported license.
Quartz
Hardness: 7
Streak: White
Chemical Formula: SiO2
Quartz is one of the most common minerals found in the Earth’s crust. While it is usually colorless and transparent, quartz can also be found in a wide variety of colors and a range of opacity. These varieties generally have their own name such as rose quartz, amethyst, smoky quartz, and citrine.
Quartz can also be found in cryptocrystalline varieties, or quartz that is made up of microscopic crystals. These varieties include chalcedony, agate, and jasper.
Gold
Streak: Golden, Yellow
Hardness: 2.5 – 3
Chemical Formula: Au
Native gold is an element and a mineral. It is highly prized by people because of its attractive color, its rarity, resistance to tarnish, and its many special properties – some of which are unique to gold. No other element has more uses than gold. All of these factors help support a price of gold that is higher than all but a few other metals.
Trace amounts of gold are found almost everywhere, but large deposits are found in only a few locations. Although there are about twenty different gold minerals, all of them are quite rare. Therefore, most gold found in nature is in the form of the native metal.
Photo: Gold by Robert M. Lavinsky is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
Pyrite
Streak: Greenish-Black
Hardness: 6 – 6.5
Chemical Formula: FeS₂
Pyrite is the most abundant sulfide mineral. It’s pale brass-yellow color is where pyrite gets its nickname “Fool’s Gold” as it was commonly mistaken for gold by novice prospectors.
The name pyrite is derived from the Greek phrase pyrites lithos, “stone or mineral which strikes fire,” due to the fact that pyrite emits sparks when struck by iron.
Pyrite is well known for it’s cuboid crystal habit, but it can also be found in many other forms. Pyrite can form dodecahedral, or twelve sided, forms known as pyritohedra.
Fool’s gold can be differentiated from real gold by its hardness, brittleness, and crystal form. Pyrite’s streak also is a defining characteristic as it is generally greenish black to brownish black whereas gold tested on a streak plate will leave a yellow streak.
Calcite
Streak: White
Hardness: 3
Chemical Formula: CaCO₃
Calcite is found commonly in ore deposits, as a cementing medium in sandstone, or in small quantities in igneous rocks.
These Calcite crystals come in a variety of sizes. Calcite can be microscopic or grow to several feet in length. It’s quite common to see excellent examples of calcite in “dogtooth” shaped crystals. These crystals have a pyramid shape. Calcite does not vary much in color. It is generally white or a pale amber.
Photo: Calcite, Dolomite by Robert M. Lavinsky is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
Author: Celeste
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