Value. Valuing boulder opal per carat is not generally accepted in the industry due to the large component of ironstone present in the stone. However, to give a rough indication, top quality boulder opal may fetch prices of up to AUD $3,500 per carat for a gem quality stone.
In this way, how are boulder opals formed?
Opal is formed from a solution of silicon dioxide and water. As water runs down through the earth, it picks up silica from sandstone, and carries this silica-rich solution into cracks and voids , caused by natural faults or decomposing fossils.
Beside above, what is a boulder opal?
Boulder opal is a rock that contains thin seams and patches of opal surrounded by or attached to its natural host rock. The cutter studies this rock and decides how to cut the best possible gem. That gem might be cut to display seams and patches of precious opal as they appear within their natural host rock.
Where do opals come from?
Opal is found around the world (Brazil, Mexico, Honduras and the western US) however Australia produces 95% of the world's precious opal and it is our official national gemstone. (see Google Arts and Culture - Australian opals).
How much is a 1 carat opal worth?
Black Opal prices vary from roughly $30 per half carat, up to $1,500 per carat. This is only the . 5-1 carat range. High quality Black Opals weighing 5-10 carats can cost up to $50,000.