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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Aussie SMOKY QUARTZ and MILKY QUARTZ - Mooralla , Victoria - 5x3.3x2.3cm NICE

AU $10.00
End Date: Sunday Sep-17-2017 21:39:30 EST
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Spiritual Rainbow! Natural Citrine quartz fantastic inclusion crystal point

AU $74.90
End Date: Monday Aug-28-2017 17:34:40 EST
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GREEN TOURMALINE IN QUARTZ - Minas Gerais, Brazil 5x3x2cm Verdelite Nice

AU $12.00
End Date: Saturday Sep-16-2017 14:49:48 EST
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Phantom Quartz From China 78Ct

AU $4.25 (0 Bids)
End Date: Sunday Aug-20-2017 11:40:24 EST
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BEAUTIFUL AGATE/QUARTZ GEODE SPECIMEN BOOKENDS, DISPLAY PIECE

AU $115.00
End Date: Thursday Sep-14-2017 21:05:19 EST
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Australian Natural Gold Quartz Specimen 68 Grams

AU $5,000.00
End Date: Tuesday Sep-12-2017 20:09:15 EST
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HERDERITE on TABBY QUARTZ - Pakistan - 7x4.5x3cm 84grams NICE

AU $35.00
End Date: Saturday Sep-9-2017 15:04:12 EST
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Some of the common varieties of chalcedony are:

   

Chalcedony specimens now available (at eBay):

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373ct/74g Pink STILBITE on CHALCEDONY Stalactite Mineral Display Specimen CS327

AU $16.99 (0 Bids)
End Date: Saturday Aug-19-2017 21:08:16 EST
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11g Blue Chalcedony w/ Mordenite Stalactite Mineral Specimen Zeolite India C517

AU $9.99 (0 Bids)
End Date: Saturday Aug-19-2017 21:02:11 EST
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63.5ct/12.5g Grey Chalcedony Stalactite Crystal Mineral Display Specimen C501

AU $10.99 (0 Bids)
End Date: Saturday Aug-19-2017 20:35:51 EST
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143.5ct/28.5g Orange Scolecite w Chalcedony Mineral Display Specimen SE7038

AU $16.99 (0 Bids)
End Date: Saturday Aug-19-2017 20:18:41 EST
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82.5g Yellow Apophyllite on Chalcedony Mineral Specimen Zeolite India AC413

AU $12.99 (0 Bids)
End Date: Saturday Aug-19-2017 20:14:27 EST
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436ct/87g Pink STILBITE on Botryoidal CHALCEDONY Mineral Display Specimen CS310

AU $18.99 (0 Bids)
End Date: Saturday Aug-19-2017 20:08:18 EST
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342ct/68.5g STILBITE & HEULANDITE w/ CHALCEDONY Mineral Specimen Zeolite HS827

AU $16.99 (0 Bids)
End Date: Saturday Aug-19-2017 20:01:36 EST
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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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From Oz VERY RARE Beautiful Opal Specimen from Vintage Rock & Fossil Collection

AU $199.95
End Date: Monday Aug-28-2017 16:35:58 EST
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1.2 kg Bolder Opal Specimen From Queensland Australian Opal lot of 32 Rough

AU $10.00 (0 Bids)
End Date: Thursday Aug-24-2017 21:00:29 EST
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Yowah Nut Material Australian Boulder Opal Unpolished Gemstone Specimen RP914

AU $195.00 (0 Bids)
End Date: Tuesday Aug-22-2017 10:05:04 EST
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Beautiful West Australian green opal with magnesite slab mineral specimen

AU $90.00
End Date: Tuesday Sep-12-2017 17:48:31 EST
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OPALS [Ward] Black + Boulder + Light Opal, Crystals, Fossils, Mexican 1stEd 1997

AU $28.25
End Date: Saturday Aug-26-2017 20:30:58 EST
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AUSTRALIAN BOULDER GREEN OPAL SOLID STONE NATURAL GEM CUT 4.90 cts + Vid

AU $100.00
End Date: Sunday Aug-20-2017 15:53:40 EST
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White Opal Natural Solid Cabochon Gem Stone (EA5677) Cooper Pedy Australia

AU $39.80
End Date: Tuesday Sep-5-2017 11:20:11 EST
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