The Varieties of Silica:
Quartz, Chalcedony & Opal

Quartz, chalcedony and opal are all forms of silica (SiO2). The difference is that quartz has visible crystals whereas chalcedony crystals can only be seen under a microscope and opal has no crystals at all.

Quartz is, by far, the most common mineral on earth. 

There are hundreds of varieties of quartz, chalcedony and opal, mostly distinguished by their color.

 

Some of the more common varieties of quartz are:

 

Quartz specimens now available (at eBay):

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EXCELLENT QUARTZ CRYSTAL CLUSTER SOURCED FROM ARKANSAS IN THE UNITED STATES

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259gBeautiful natural yellow - skinned chrysanthemum - like quartz mineral

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Mineral Specimens 2.5kg Mixed Minerals 73 total Quartz Agate Opal

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Some of the common varieties of chalcedony are:

   

Chalcedony specimens now available (at eBay):

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Chalcedony Nodule Morocco 160805 41mm Stone of Brotherhood Healing Metaphysical

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Chalcedony Nodule Morocco 160807 33mm Stone of Brotherhood Healing Metaphysical

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Chalcedony Nodule Morocco 160803 44mm Stone of Brotherhood Healing Metaphysical

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Chalcedony Rosette Specimen Stone of Brotherhood Metaphysical-160110

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Blue Chalcedony Specimen Stone of Brotherhood Metaphysical Healing-160124

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Chalcedony Nodule Morocco 160802 48mm Stone of Brotherhood Healing Metaphysical

AU $5.20
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Chalcedony Rosette Specimen Stone of Brotherhood Metaphysical-160107

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Some opal displays different colors when viewed from different directions. Any opal which exhibits this play of colors is called "precious opal"; opal which does not exhibit a play of colors is called "common opal". Some of the common varieties of opal are:

Opal specimens now available (at eBay):

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Polished Pink Opal Smooth Palm Stone 180623 36mm Peace and Tranquility

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Polished Pink Opal Smooth Palm Stone 180624 34mm Peace and Tranquility

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Polished Pink Opal Smooth Palm Stone 180628 41mm Peace and Tranquility

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Polished Pink Opal Smooth Palm Stone 180625 39mm Peace and Tranquility

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Green Apple Pistachio Opal Freeform Palm Stone 181205-53mm Mineral Miner

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Boulder Opal Rough Stone Natural Solid Koroit Yowah Australian 81 Carats tcw

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Green Apple Pistachio Opal Freeform Palm Stone 181204-70mm Mineral Mineraloid

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