Fine #boulder #matrix #opal often has attractive banded ironstone or patterns. Sometimes the opal forms in a central kernel within a small boulder. These are known as ‘nuts’ and are commonly found at the Yowah and Koroit fields.

Black #OpalsBlack opal is a generic term given to any opal which has a dark body colour when viewed from above. "Play of colour" within a dark or black body colour will enhance the brilliance of the colours.
Some have a transparent crystal colour bar overlaying dark opal, giving the otherwise light opal a dark appearance.

Black opals range from opaque to transparent crystal colour bar overlaying dark #opal.

Boulder OpalsFine grade boulder opals have the top surface covered with precious opal. Slight marks and protrusions of ironstone in the face of the stone are fairly typical, and can affect value. Boulder opal is usually cut to the contours of the opal vein creating a baroque wavy surface and they are often irregular in shape. The most expensive boulder opals are those with a dark body tone and displaying a full face of brilliant precious opal.

Light #OpalsLight Opal is commonly referred to as “white", although this term should be used only where the body colour is milky or white. It should not be used to describe the entire light opal family.

Light #opal makes up the bulk of precious opal and comes from all fields but the majority is found in South Australia. Brilliant light opal can be extremely valuable. The transparent material (crystal) variety commands the highest price.