Reference:

ABOUT OPALS

What is a Black Opal ?

A black opal is a natural solid stone with a black or nearly black body tone (ie background appearance).

Whether an opal is a black or not can be determined by nearly closing ones eyes and squinting at the face of the stone. All colours are ignored and the overall body tone (blackness level) can then be seen. When this is compared to the scale of blackness given in Figure 1 below it is possible to identify how black the stone is.

Only stones achieving values N1 to N4 on this scale are considered black opals - attracting the additional value associated of this class of opal.

Black Opal	Dark Opal	Light Opal

Black opal

Precious opal that has a black appearance when viewed from the front. Only opal that looks as dark as the N1-N4 body tone scale (below) can be truly called a black opal.Rarer than light or dark opal

Usually Lightning Ridge area in NSW or more rarely Mintabie in South Australia

Find more information at the OPAL Association's Opal Nomenclature Section of their Website:

http://www.opal.asn.au/information_nom