When the opal is mixed through the ironstone it is called matrix opal. Hardness ranges between 5.5 and 6 on the scale.  Boulder opal is very durable due to the ironstone backing the opal forms on. Because water content within the opal is very low it almost never cracks or crazes as it ages.

There are two distinct types of opal, common and precious. The way the silica particles form determines which type. In precious opal, silica particles are packed in regular rows and layers. Moving the stone causes light to diffract, or split, as it grazes the opal surface. This light diffusion shows iridescent flashes of green, blue, aqua and sometimes yellowish or red colors which are referred to as "fire".


Color and Varieties:
Black Opal is the most rare and valuable opal. Fine quality black opals often cost more per carat than diamonds. The term black opal is misleading because the opal is not actually black, but instead has a very dark base. This dark base enhances the brilliant colors known as "fire".

Boulder opal forms on a dark ironstone base (the host rock) and occurs as a thin uneven layer adhering to the ironstone. Because of the uneven layers, sometimes part of the ironstone is visible on the surface of the stone. Opals can form anywhere but are mostly found in places where there hot springs. It is sedimentary and is fluorescent a lot of times. It is a very easy stone to break.  Opals are mined using open pit surface mining.

Light opal is the most common type of opal found and refers to both the crystal type opal (translucent) and the milky opal (opaque). It is the most common variety of opal and is generally less expensive than gem quality light opal. Brilliantly colored light opals may be quite expensive with a value exceeding some Black and Boulder Opals.

Brilliance or luster is one of the primary factors that determine an opal's value. An opal with strong intensity and color play adds more value.

Aids inner beauty, faithfulness, and eyesight and helps recall past lives.
It is believed opal was the symbol of hope and purity and kept the wearer safe from disease.
It was also believed the opal had the power of giving foresight and the light of prophecy to their owners