Why is opal not a mineral

Therefore opal is a "mineraloid" rather than a "mineral." These items of jewelry normally do not receive significant abrasion and impact during wear. Because opal does not have a crystal structure, it is classified as a mineraloid—a mineral-like substance without well-formed crystals. Precious opal (not. Back to Rocks and Minerals Articles Suzanne Paradis, Geological Survey of that could befall one for wearing opal if it were not the wearer's birthstone.