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Chemical Formula: SiO2
Agate is a common form of chalcedony, a microcrystalline form of quartz. It’s banded, colorful appearance has lead to its widespread use throughout human history.
Most varieties of agate are named for its visual appearance, such as fire agate which has inclusions of red or brown hematite. Agate can also vary in its banding appearance, some agates have a dendritic habit or lace-like patterns with eyes, swirls, and other patterns.
Because this mineral is a form of quartz, it’s hardness lends itself to uses not commonly associated with such visually appealing minerals. Agate has been used to create precision pendulums, mortars and pestles, and fine knife-bearing edges for laboratory balances.
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.
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.
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.
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.
Chemical Formula: CaCO3
Pearls are an organic mineral formed inside a mollusk. The mollusk takes aragonite, the same mineral that makes up its shell, and builds up concentric layers around any foreign particle that enters the mollusk’s mantle.
Pearls vary widely in color and shape, depending on its environment and also the shape of the foreign object that entered the mollusk. Farmed pearls achieve their perfect, spherical shape by planting perfectly spherical “seeds” into the shells and allowing the mollusk to build up only a small amount of aragonite secretions to cover the item.