Gemstones - Precious Gems
Opal
Opal is one of those gems that has a unique makeup and a unique following. But most who have never been captivated by the gems from down under have never studied a top quality black opal.
The presentation of color in opal is unique. So is the fact that opals need to mainain their water content.
Besides the normal care required of opal, the gemstone is soft. And opals are not durable. They break and scratch easily and so bezel setting is normal. It is also common to see opals set so that the surface is below the edge of the bezel.
Opals are amorphous, meaning that they have no definite crystalline form. The play of color from an opal is ligh reflected and refracted from groups of microscopic spheres. The size of the spheres determines the color of light they display.
Dehydration is a problem with opal and may cause crazing or checking.
Properties of Opal
- Crystal System - amorphous
- Hardness - 5.5 to 6.5
- Specific Gravity - 1.98 to 2.2
- Refractive Index - 1.757 to 1.779
- Wearability - fair
- Special Care - Drying is a problem