What Is Semi-Black Opal?

by Anne Ongemann

A Semi-Black Solid Opal

A Semi-Black Solid Opal

I have become increasingly fascinated by opals and am trying to learn as much as possible about them.

I have bought some beautiful solid black opals,which are translucent, and know about the body tone scale and that 1 is darkest and seven (7) lightest in basic body colour, but I keep coming across the term "semi black" opals.

So what exactly is semi black?

Is it a recognized and valid term of description, or is it a bit of a sales trick.....or something else entirely?

I also get them impression that the term "crystal" is not standardized.

I would be really glad to get some information on this.


Hello Anne,

Thank you for your question and allowing me the opportunity to explain exactly what constitutes a semi-black opal.

No.. it is not a sales trick (!) but a legitimate grading of body and colour tone opal category.

True black opal grading stops at the N4 tone, whereas semi-black opal or otherwise termed "dark opal" ranges within the N5 and N6 category.

N7 would be classed as dark grey, N8 would be light grey and N9.. white opal.

1) An opal may be classed Semi-black where opal crystal sits on a N5 to N6 dark base and therefore deepens the body tone of the colours.

2) Where the gem opal is naturally integrated within the base stone itself and that base stone is in the N5 to N6 category, then that opal too constitutes a semi-black opal.

3) Alternatively, where solid crystal is not attached to any dark coloured base and has it's own distinct darkish tone and this dark tone falls within the N5 to N6 category, then this type of gem can also be classed as a semi-black gemstone.

In summing up;

Crystal Opal types - true crystal opal is like water-clear quartz crystal filled with pure clean colour.

Semi-crystal - is where the body tone of the opal can still be translucent, but not quite water clear and then it ranges from semi-crystal white base through to white opal (which is a white coloured base stone with the opal colours formed within the base opal itself).

I hope this has helped to make things a little easier to understand with the different grading of semi-black opal types and thank you again for your question.

Kind regards,

Click here to view Our Black Opal Solids

Click here to post comments

Join in and write your own page! It's easy to do. How? Simply click here to return to Opal Questions.