Due to the formation of opal, it is often formed as sub-microscopic spheres that are stacked in a grid-like pattern. The precious type of opal is very different though, with a wide array of colors within a single specimen. Common opal doesn't have a wide array of fantastical colors and typically can be confused for quartz or chalcedony. There are two types of opal, common and precious. After the water evaporates, the water imbued silica is left behind, forming opal. The rain soaks into the ground surface, carrying with it dissolved silica. Another primary property of opal is that it has a hardness on the Mohs Hardness Scale of 5.5 to 6, making it much softer than most gemstones (quartz is a 7). Opal forms from the seasonal rains that drench dry grounds in desert regions. Also, since opal can have varying amounts of water (the 'n' in the chemical formula), this actually makes is a mineraloid, and not a true mineral (minerals have a set chemical formula). And while quartz is often found in crystals, opal is amorphous, meaning it has no crystal structure. Opal on the other hand can often come in a wide range of colors, anything in the rainbow and beyond really, all within a single sample. white, pink, purple, grey, clear), the colors within a crystal of quartz are usually pretty consistent. Although quartz itself can come in a variety of colors (i.e.

Opal then could be considered the hydrated form of quartz, however the water ends up making the properties of opal very different from quartz. Silica, SiO2, is more commonly known as quartz, and is one of the most common minerals on the planet. The chemical composition of opal is a hydrous silicon dioxide (SiO2. State Precious Gemstone: Virgin Valley Black Fire Opal Indiana Jones and the Chronology of Chaos.

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