Hyalite
Have a closer look at this fascinating gem. Hyalite is a clear, glassy form of opal that looks like a drop of water. It’s often completely transparent and can glow green under UV light.
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Geology Science
One of the most striking features of hyalite opal is its ability to exhibit strong green fluorescence under ultraviolet light. This fluorescent quality is due to trace amounts of uranium within its composition, making it one of the few gemstones that naturally fluoresce.
Geological Conditions for Formation: Hyalite opal forms under specific geological conditions where silica-rich solutions are present. These conditions typically occur in volcanic regions where silica can leach out from volcanic ash layers and dissolve in water. Over time, this silica-saturated solution can infiltrate cavities, cracks, or spaces around rocks and gradually deposit hyalite opal as the water evaporates or cools. The formation process involves a slow accumulation of silica gel which eventually hardens into hyalite opal, trapping water molecules within its structure.
Major Global Locations: Hyalite opal is found in several key locations around the world, primarily associated with regions that have a history of volcanic activity. Some of the notable places where hyalite opal occurs include:
- Mexico: Known for producing high-quality hyalite opal, especially in regions around Central Mexico where volcanic activity has historically been prevalent.
- United States: Specific locations in Arizona, California, and Nevada are known for their deposits of hyalite opal, often found in areas with past geothermal or volcanic activity.
- Germany: The Eifel region in Germany is another well-known area for hyalite opal, again linked to its volcanic past.
- Australia and New Zealand: Both countries have regions where hyalite opal can be found, associated with their volcanic zones.
These locations all share common geological traits, such as past volcanic activity and the presence of silica-rich rocks, which are conducive to the formation of hyalite opal. The presence of hyalite opal in these regions underscores the mineral’s close association with specific and unique geological settings that provide the necessary conditions for its development.
Find out more from Geology Science here
Gem-A - Beginner’s Guide: What Are the Different Types of Opal?
by Charles Bexfield
There are many more varieties of common opal but two other important varieties are fire opal – this is the intense orange colour opal – and hyalite, the translucent variety of opal that doesn’t display a play of colour.
Gem Select: Hyalite Opal Gemstone Information
Hyalite Opal SpeciesHyalite is a variety of Opal which does not have the internal mineral structure made of tiny spheres that cause the play-of-color that makes other Opal varieties so valuable.Its official name these days is Opal-AN. The A stands for Amorphous meaning it does not have a definite or distinct shape and the N stands for Network to point out the structure of the opal is more like a silica network than the collection of spheres that make up most opals.By the way, Opals that display the famous play-of-color have regular stacking of spheres in their physical internal construction are technically Opal-AG.
Hyalite Opal is an extraordinary object being a very rare variety of a rare gemstone. While other members of the opal family create an amazing play-of-color using diffraction and interference of light bouncing around sub-microscopic spheres, Hyalite uses uranium to give off its ghostly glow.
Hyalite Opals occur in volcanic and magma created igneous rock formations. Water and silica were introduced into the rock formations when they were still very hot and formed globular and irregular crusts as they cooled.
The water dehydrated and the silica left a gel which solidified over millions of years. Elements such as iron, magnesium, aluminum and, in the case of fluorescent Hyalite Opals, uranium were introduced into the mix.
Find out more from Gem Select here
Hyalite in images from Harmony Gems
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