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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Quartz "Faden" Dara Ismael Khan Waziristan Pakistan

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Quartz Crystal bulk lot x10, Tingha NSW Australia

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192.5g Large Smoky Black Quartz Crystal Point Cluster Mineral Specimen Q95

AU $39.99
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Tourmaline in Quartz Crystal cluster, Wallangra NSW Australia.

AU $15.99
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7pcs Tourmaline in Quartz. Tumbled/polished Wallangra NSW Australia.

AU $8.99
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Pineapple Candle Quartz Crystal bulk lot x10, Copeton NSW Australia (L91)

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Quartz Rock Crystal bulk lot x10, Copeton NSW Australia (L89)

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Some of the common varieties of chalcedony are:

   

Chalcedony specimens now available (at eBay):

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blue chalcedony lapidary slab

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Fluorapophyllite with Chalcedony Jalgaon district Maharashtra India

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Chalcedony on Calcite? Nashik district Maharashtra India

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314ct/63g Milky STILBITE CHALCEDONY & SCOLECITE Mineral Display Specimen S704

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Fluorapophyllite on Chalcedony Jalgaon District Maharashtra India

AU $20.00 (1 Bid)
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54ct/11g Small White Chalcedony Stalactites Mineral Display Specimen Zeolite

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115ct/23g Sugary White Chalcedony Mineral Display Specimen Zeolite - C515

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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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Queensland Boulder Opal Specimen

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RAW BOULDER OPAL 69 Х 49 X 30 MM 107 G

AU $26.00
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Andamooka Natural Matrix Opal Specimen 24 15 05 20

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Andamooka Natural Matrix Opal Specimen 26 15 05 20

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Andamooka Opal Rough All Pieces Have Color 11 15 05 20

AU $45.00 (1 Bid)
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Andamooka Natural Matrix Opal Specimen 19 15 05 20

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Andamooka Natural Matrix Opal Specimen 15 15 05 20

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