Hardness: 2 – 2.5
Chemical Formula: C137H97O9NS
Bituminous Coal is one of the four recognized varieties of coal. It is the most abundant and it frequently used for heat generation, but it not as efficient as Anthracite Coal which is the highest grade of coal.
Bituminous Coal is relatively soft and contains the tar-like substance asphalt or bitumen. It is generally black in color or dark brown, featuring well-defined bands of bright and dull material.
Coal in general is an organic sedimentary rock formed from the fossilized remains of plants. It generally occurs in layered, sedimentary deposits.
Hardness: 2.5 – 3
Chemical Formula: Cu
Copper is one of the few metals with a natural color other than gray or silver. When it is pure, copper is a rose color, but it quickly tarnishes and later oxidizes after time in the air. This tarnish creates the green color the copper is known for.
Copper crystals are incredibly rare and copper is most often found in irregular or branching masses.
Copper is thought to be the oldest metal in use, with examples of early use being found as early as 8000BCE. By 3500BCE, copper was being mixed with tin to create bronze, ushering in the Bronze Age.
Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate. It is very widely mined and used in a huge variety of industries from Ancient Egypt to modern day. Gypsum is used in everything from drywall to fertilizer, in removing pollutants from water, and even in baking.
Gypsum can also crystallize and be found as translucent crystals of selenite. The fine-grained white variety of gypsum called alabaster is prized for its ornamental uses. It is soft and often used for carving.
Another form of gypsum is the desert rose, a flower-like form, typically opaque, with embedded sand grains.