Rocks

Most specimens in this website are minerals. A mineral has a chemical formula, it may have crystals of a particular shape, and it's all basically the same. Rocks are mixtures of minerals, and tend to occur in large quantities, such as a whole mountain. They don't have formulas, as the combinations of elements vary throughout the rock.

Building stone

Limestone

Sandstone

Flint

Slate

Granite

Other rocks

Obsidian

Pumice

Marble

Serpentine

Stonehenge

Blue Lias

Chalk

Coal