Physical Properties Of The Black Opal Stone Mineral Group Some dark grey or dark green opals are sometimes referred to as black opals this is a miscategorization. The internal structure of this precious opal makes it diffract light. The water content of this stone may range from 3 to 21% by weight, but usually, it’s around 6 to 10%. The effect is similar to that of a rainbow or oil on water.īlack opal is a hydrated amorphous form of silica, typically found in sedimentary rocks. The play of color in a black opal is due to light diffraction in the thin, transparent layers of the stone. The most valuable black opals are called “black fire” because they display a play of colors, like reds and greens (such as sunlight or candlelight). Black opals are also characterized by their play of color, which may be seen when moving the stone or in different lighting conditions. ![]() ![]() The stone’s color is not the only thing that makes it valuable. They may be transparent or translucent, but this is rare. Black Opal Stone Appearanceīlack opals are usually opaque and usually have a completely black body tone. “Opal” is also derived from the Greek word opallios, which means “to see a change of color.” This refers to the way light passes through an opal and causes it to change colors. “Opal” comes from the Sanskrit word upala, meaning “precious stone.” What Does The Word Opal Mean (Etymology)? Because opals are porous, they can hold water and other small molecules, making them susceptible to degradation. The result is a beautiful, shimmering stone that can be cut into many shapes.Ĭrystal opal is a form of silica gel, an amorphous hydrated silicon dioxide. ![]() Finding large pieces of Black Opal gemstone is also challenging because they are usually cut into smaller stones. Black Opal is one of the rarest among different opal types, as it takes a great deal of time for the silica gel to form.
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