graeme
Onyx is often confused with marbles due to is flowing and veiney appearance. yet it is a different rock type. Onyx is a sedimentary rock, formed as stalactites and stalagmites in cave interiors. This formation method results in the cryptocrystalline construction of the rock fabric, and it is the size and uniformity of these crystals that contribute to the classic translucent property of most onyx varieties. I believe its the only or one of a few rocks that allows light to pass through so when used in panels and walls with light behind, it looks great.
It registers about 6 or 7 on the MOHHs scale and is vulnerable to chemical and abrasive attack, similar to marbles, but can be restored in similar way, by grinding a polishing.
Kevin may correct me on some of the info, as its not a material we come across that often in houses, apart from 1 fireplace we did.
