Opal essence

Sandy Grimm took this eye-popping picture of an opal (Accession No.: 28.2006) at the Houston Museum of Natural Science for Wikipedia Loves Art. According to Grimm's photostream this opal is one of the largest and finest quality boulder opals ever mined and "is unique not only for its size but for its quality – every color of the spectrum is visible, which is extremely rare."

The museum's web site offers:

• The word opal is derived from the Sanskrit upala, the Greek opallios, and the Latin opalus, meaning “precious stone.” Some cultures believe it to bring good luck, while others claim that wearing it is unlucky.


• Opal is a mineraloid, as it does not have a crystal structure. Precious opal is composed of closely packed spheres of silica. The multi-hued colors of opal are caused by the refraction of light passing through this microstructure.


• Opal has been mined for centuries. The Romans extracted it from the area that is the Czech Republic today; the Aztecs made use of local sources in Mexico and the Spaniards exported those opals to Europe. Today, approximately 95 percent of the world’s opal supply comes from Australia.