Opal
Opal is a hydrated amorphous form of silica (SiO. ... Because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classed as minerals.
Opal is a hydrated amorphous form of silica (SiO. ... Because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classed as minerals.