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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Star Hollandite (Black Star Quartz, Star Quartz, Spider Quartz) 5.67grams

AU $12.50
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48g 8pcs Rainbows Aura Quartz Crystal Titanium Bismuth Silicon Points specimen

AU $2.25 (4 Bids)
End Date: Wednesday Feb-28-2018 18:15:38 EST
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Candle Quartz Crystal Cluster 137g

AU $50.00
End Date: Monday Feb-26-2018 23:25:42 EST
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41g Rare Natural Extreme transparent blue phantom Fluorite & Quartz specimen

AU $15.50 (12 Bids)
End Date: Monday Feb-26-2018 16:45:24 EST
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143g Natural Translucent Trapezoidal deep Purple Phantom Fluorite

AU $2.25 (3 Bids)
End Date: Monday Feb-26-2018 16:44:09 EST
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356gRare Natural Transparent Trapezoidal Purple Phantom Fluorite

AU $10.50 (7 Bids)
End Date: Monday Feb-26-2018 16:41:13 EST
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Some of the common varieties of chalcedony are:

   

Chalcedony specimens now available (at eBay):

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Chalcedony - Redcliffe Qld

AU $6.50 (0 Bids)
End Date: Wednesday Feb-28-2018 21:18:09 EST
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157.5ct/31.5g Stilbite Chalcedony Apophyllite Mineral Display Specimen ASC237

AU $9.99 (0 Bids)
End Date: Sunday Mar-4-2018 19:24:53 EST
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423.5ct/84.5g Chalcedony Stilbite Mordenite Geode Mineral Display Specimen CS336

AU $12.99 (0 Bids)
End Date: Sunday Mar-4-2018 19:15:31 EST
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Blue Chalcedony bubbly 116g 9cm x 6cm

AU $50.00
End Date: Wednesday Feb-28-2018 3:33:53 EST
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183.5ct/36.5g Chalcedony Stalactites w/ Pink Stilbite Mineral Specimen - CS307

AU $14.99 (0 Bids)
End Date: Thursday Mar-1-2018 22:39:20 EST
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314ct/63g Milky STILBITE CHALCEDONY & SCOLECITE Mineral Display Specimen S704

AU $14.99 (0 Bids)
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82.5g Yellow Apophyllite on Chalcedony Mineral Specimen Zeolite India AC413

AU $12.99 (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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Beautiful COOBER PEDY [Opal Capital of the World] intact perf'd 4 postcard sheet

AU $19.95
End Date: Friday Mar-23-2018 22:20:46 EST
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AUSTRALIAN GEMSTONES IN COLOUR HandB 41 gemstones + origin opal color PERRY 1973

AU $15.25
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THE OPAL BOOK Leechman HB 5th Edn guide+maps WhiteCliffs LightningR CooberP Anda

AU $17.95
End Date: Friday Mar-23-2018 21:20:50 EST
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crystal opal carved fish

AU $350.00
End Date: Thursday Mar-22-2018 13:06:47 EST
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Opal Rock

AU $63.99 (0 Bids)
End Date: Monday Feb-26-2018 20:00:56 EST
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