There are very few gemstones that have a luster that deserves to be called adamantine. Diamond is one, of course; the rare demantoid garnet is another (the name 'demantoid' means 'diamond-like'). But one of the members of this exclusive group is a gem that few people have heard of, and even fewer have seen; sphene.
Sphene is a very rare brilliant yellowish-green, green, orange or brown gemstone with a high lustre, also known as "titanite" due to its titanium content. Due to its strong dispersion, when brilliant-cut, sphene can exhibit a fire similar to that of diamond.
This is the famous, now depleted, Capelinha Sphene! very sought after and rare. this pear shaped shene is 1.28ct and of a apale lime green/ yellow colour. the clarity is good and it is flanked by 6 VS clarity diamonds ( 3 on each shoulder). Set into 2.24g of 18k yellow gold it has the fire that sphene is so famous for.
This ring is a an average ring size N or US 7