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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White Quartz cluster specimen, Ashton Quarry South Australia

AU $64.50
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Fluorite "ball" with Calcite on Quartz Nasik district Maharashtra India

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Fluorite on Quartz with Pyrite Yaogangxian Mine, Hunan province, China

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Calcite with Sphalerite, Galena & Quartz Nicolaevsky Mine Dal'negorsk Russia

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Fluorite on Quartz Second Soviet Mine Dal'negorsk Russia

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Scheelite on Quartz Yao Gang Xian Chenzhou Hunan Province China

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Quartz - Variety: Amethyst on Sphalerite Naica Chihuahua Mexico

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Some of the common varieties of chalcedony are:

   

Chalcedony specimens now available (at eBay):

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

AU $12.99 (0 Bids)
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54ct/11g Small White Chalcedony Stalactites Mineral Display Specimen Zeolite

AU $9.99 (0 Bids)
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115ct/23g Sugary White Chalcedony Mineral Display Specimen Zeolite - C515

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Fluorapophyllite on Chalcedony Jalgaon Maharashtra India

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Chalcedony "stalactite" Nasik Maharashtra India

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DRUSY QUARTZ & CHALCEDONY MINERAL SPECIMEN - CAPELLA QLD

AU $15.75 (0 Bids)
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NATURAL CHALCEDONY DRUZY FOSSILIZED SHELL PENDANT BEAD RAREST NEW MATERIAL 1.8"

AU $101.67
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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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Andamooka And Coober Pedy Opal Rough All Pieces Have Color 06

AU $45.00 (1 Bid)
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Andamooka And Coober Pedy Opal Rough All Pieces Have Color 08

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Andamooka And Coober Pedy Opal Rough All Pieces Have Color 02

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Scarce Andamooka Electric Blue Fluorescent Opal Phenomenon

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Andamooka And Coober Pedy Opal Rough All Pieces Have Color 07

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Precious Australian Opal Rough Slices With A Chip Or Two

AU $115.00 (2 Bids)
End Date: Sunday Apr-12-2020 16:18:46 EST
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