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What is Chalcedony Gem

What is Chalcedony. It is a Gemstone


It is a gemstone, belongs to the quartz group of minerals.

Gemological Term.

Chalcedony is the gemological term applicable for all varieties of quartz in Cryptocrystalline form.

Different Colours.

Chalcedony occur in a wide range of different colours, sizes and patterns

Chalcedony, is most often used in reference to a very specific type of Cryptocrystalline quartz.


Chalcedony Quartz

Chalcedony  including agate, chrysoprase, carnelian, bloodstone, jasper, onyx, moss agate and petrified wood. So all quartz that is not macrocrystalline, such as amethyst, citrine, rock crystal and smoky quartz, is referred to generically as chalcedony.

Chalcedony is also used as a varietal name to refer specifically to bluish-gray or lavender colored cryptocrystalline quartz. This color is sometimes called “actual chalcedony” or “chalcedony in the narrow sense”.  Other chalcedony is referred to by other names, such as agate, bloodstone or carnelian.

Chalcedony is most often cut as cabochons and with its good hardness.  A wide variety of colors are available; the most well-known include red-orange (carnelian), apple-green (chrysoprase), blue or lavender (chalcedony), black (onyx) and deep green with red (bloodstone or heliotrope).

Chalcedony Gemstone Jewellery

As the defining mineral for 7 on the Mohs scale, chalcedony quartz is known to set the standard when it comes to gemstone hardness for jewellery gemstones.

Chalcedony Polish.

Chalcedony is known to take an excellent polish, in fact, after a prolonged polish, some chalcedony varieties can exhibit a glow that seems to emanate from within. Chalcedony quartz is without a doubt one of the most significant materials of all time.

Identify Chalcedony.

Some of the most popular chalcedony varieties are identified as follows:


Agate is distinguished by having multiple colors.

Lots of Different Agate.

There are countless varieties of agate available, with banded agate being the most popular and well known agate variety. One of the rarest types of agate is ‘fire agate’, which exhibits an iridescent property, reflecting colors of red, gold, green and blue-violet. Other popular agates include agate jasper, agate geode, dendritic agate, tree agate, Botswana agate, blue lace agate, fossil agate, iris agate, laguna agate, landscape agate, scenic agate, tube agate, snakeskin agate, Sweetwater agate, Mohave blue agate, thunderegg agate, Fairburn agate, Dryhead agate and Lake Superior agate.

Agate often fills cracks or veins in volcanic rock, or cavities in cooled lava – it can even be found in dinosaur bones. Many agates do not fill completely, in which case druzy Quartz Crystals can form in the centre . In fact, sometimes amethyst crystals will form.

Australia Agate.

In Australia we have agate, there is a fossicking area called Agate Creek, in North Queensland. I have been there. At first I did not know what I was looking for. When we finally stop and got out of the car , and had a look around. We soon found what a agate stone looked like. The people before us had smashed hundreds of rocks. There were rock with coloured lines through them, ( all Colours). Also ones with Crystals in the smashed rocks. We found some hole rocks, the small whole rocks I picked up, easy to tumble and they look good in pot plants.

Agate from Agate Creek.
Gooseberry Agate.





Rough Bloodstone


Bloodstone is an opaque, dark-green chalcedony with red to brown spotting caused by iron oxide. Some may exhibit yellow spotting, which is known as ‘plasma’ in the gem trade.

Black Onyx  Stone


Onyx is the most traditional black gemstone.

Onyx is a layered stone with a black base and a white upper layer. Uni-colored chalcedony is sometimes called onyx.

Most people think of onyx as a black gemstone.

In the gemological world, the term onyx refers to layered stones that exhibit different colors in multiple layers. Usually this material is cut from agate or other types of chalcedony with even, parallel layers, usually with a lighter layer above a darker one.


Onyx is similar to other cryptocrystalline quartz, with a hardness of 6.5 to 7 on the Mohs scale. Like all quartz, it is silicon dioxide with a density of 2.58-2.65 and a refractive index of 1.530-1.540.

How are Macro- and Cryptocrystalline Quartz Different?

How is Macrocrystalline quartz different from the Crypto- and Macrocrystalline forms of quartz?

Outside appearance.

Macrocrystalline quartz like amethyst and rose quartz are generally transparent-translucent.

Cryptocrystallines like agates are more often opaque.

Agates and Cryptocrystallines can be slightly softer than Macrocrystallines, 6.5 on Moh’s scale rather than a full 7. Cryptocrystallines have a duller, wax-like luster.

Macrocrystallines have a shiny, vitreous luster.

Cryptocrystallines have a higher water content as well as other non-quartz ingredients, up to 20% more.









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