Natural Ethiopian Opal Pictures taken with high resolution camera on different backgrounds in order to depict the item as realistically as possible. International registered mail with tracking number. Description An opal is a hydrated form of silica with a water content ranging from 3 to 21%.Indeed, it is this permeability to water that makes it a hydrophile. Opals are deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl, and basalt. Precious opals show a variable interplay of internal colors. Hydrophane Opals A category of opals is the hydrophane. The hydrophane opal is a particular variety of opal that, having lost its water, appears murky and insignificant. It is, however, surprising what happens to this stone when it is immersed in water (time varies from minutes to some days): its refraction index goes from 1.40 to 1.44 and being rehydrated is almost unrecognizable due to its newly found almost impeccable transparency and splendid hues of iridescence. However, this treatment is skin-deep. When referring to the hydrophane opal, we’re therefore talking about a category of this mineral that is not sparkly, is highly porous and becomes transparent when immersed in water.