Commodity Code

opal

http://resource.geosciml.org/classifier/cgi/commodity-code/opal

definition Opal is a hydrated amorphous form of silica; its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Because of its amorphous character, it is classed as a mineraloid more like this
notation
01.03.29.02 more like this
Opal more like this
source http://en.wikipedia.org/wiki/Opal more like this
type
Resource
Concept
broader silica gemstone
narrower opal
in scheme commodity code
is primary topic of opal