Muscovite Mica

Streak: White

Hardness: 2 – 2.5

Chemical Formula: KAl2(AlSi3O10)(F,OH)2

Muscovite is the most common mineral of the mica family. It is an important rock-forming mineral present in igneous, metamorphic, and sedimentary rocks. Like other micas it readily cleaves into thin transparent sheets. Muscovite sheets have a pearly to vitreous luster on their surface. If they are held up to the light, they are transparent and nearly colorless, but most have a slight brown, yellow, green, or rose-color tint.

Photo: Muscovite Mica by James St John is Licensed Under the Creative Commons Attribution 2.0 Generic license.

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.

sample of smoky quartz

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

Gold generally occurs in tree-like growths or grains. Because of it’s inert state, gold resists tarnish and is generally found in a relatively pure form.

Almost all of the gold recovered from the earth comes from placer deposits, weathered particles concentrated in river gravel. This relatively rare mineral has been used since antiquity in many facets of human life from coinage to art and beyond.

Today, 10% of the gold produced finds its way into industry with much of it being used to produce electronic components.

Photo: Gold by Robert M. Lavinsky is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

sample of pyrite

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.

Sillimanite

Streak: White

Hardness: 7

Chemical Formula: Al2OSiO5

Sillimanite is an aluminosilicate mineral with the chemical formula Al2SiO5. Sillimanite is named after the American chemist Benjamin Silliman (1779–1864). It was first described in 1824 for an occurrence in Chester, US.

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Celeste
Author: Celeste

Rocks!