There are a variety of types available, which depend on the mix of minerals and type of soil / rock that they are discovered in.

Some of these include Ironstone, Sandstone, Pipe Crystal, Yowah and Koroit Nuts, Matrix and Fairy.
Boulder opal is popularly used by jewelers around the world in pendant designs, rings, earrings and other jewelry.

They often show an array of colors from more common blues and greens to rarer colors such as rainbows and reds.

They often have an earthy, rock look.

There have also been a lot of fossilized vegetation and wood discovered, which make for some very unique looking jewelry designs.

Every piece of opal is unique; one and only.