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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239g EXOTIC SMOKY QUARTZ - LODALITE PHANTOMS polished BRAZIL MINED CRYSTAL POINT

AU $29.99
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Candle/Pineapple Quartz Crystal Cluster

AU $7.00 (0 Bids)
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Candle Pineapple Quartz Specimen, Copeton NSW

AU $7.00 (0 Bids)
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Candle Pineapple Quartz Specimen, Copeton NSW

AU $4.00 (0 Bids)
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Molybdenite on Quartz, Kingsgate NSW

AU $6.00 (0 Bids)
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Some of the common varieties of chalcedony are:

   

Chalcedony specimens now available (at eBay):

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Blue Chalcedony Pseudomorph Amazing Rare Specimen 192 Grams 6.8 Oz Gyor Hungary

AU $195.58
End Date: Thursday Mar-21-2019 4:24:47 EST
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157.5ct/31.5g Stilbite Chalcedony Apophyllite Mineral Display Specimen ASC237

AU $9.99 (0 Bids)
End Date: Sunday Feb-24-2019 22:27:51 EST
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212ct/42.5g Chalcedony Plate Geode Mineral Display Specimen India Zeolite C519

AU $9.99 (0 Bids)
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423.5ct/84.5g Chalcedony Stilbite Mordenite Geode Mineral Display Specimen CS336

AU $12.99 (0 Bids)
End Date: Sunday Feb-24-2019 22:27:51 EST
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319ct/64g Clear Apophyllite Cubes w Black Chalcedony Mineral Specimen AC418

AU $10.99
End Date: Tuesday Mar-19-2019 22:23:35 EST
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232.5g Pink Stilbite on White Chalcedony Mineral Specimen Zeolite India CS341

AU $24.99 (0 Bids)
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28.5g Pink Stilbite on Grey Chalcedony Mineral Specimen Zeolite CS340

AU $9.99 (0 Bids)
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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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OREGON OPAL NICE CLEAR SEMI TRANSPARENT BIG SPHERE TRIM 3.8 OZ or 108 GRAMS

AU $80.82
End Date: Thursday Mar-21-2019 4:24:03 EST
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Beautiful West Australian green opal with magnesite polished end piece

AU $70.00
End Date: Wednesday Mar-20-2019 15:20:08 EST
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OPAL MINING BOOK BEFORE & BEYOND 2000 WITH SURFACE INDICATIONS Stephen Aracic

AU $65.00
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CACHOLONG OPAL VARIETY COMMON OPAL109 X 81 X 53 MM 550 G

AU $34.00 (0 Bids)
End Date: Sunday Feb-24-2019 22:00:20 EST
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A+ 47mm Australian Queensland Boulder Opal Rough 234.5 carats

AU $129.39
End Date: Tuesday Mar-19-2019 8:15:45 EST
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