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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146g Natural Fluorite Quartz Crystal Sphere Ball Healing 11-11-34

AU $0.01 (1 Bid)
End Date: Saturday Dec-16-2017 13:33:41 EST
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Quartz, Citrine, Torrington, NSW (24)

AU $25.00
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Quartz Crystal Natural Gemstone Geode Pair, Bu Craa, W. Sahara, Morocco (EA7581)

AU $54.00
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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
End Date: Wednesday Jan-10-2018 20:14:25 EST
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314ct/63g Milky STILBITE CHALCEDONY & SCOLECITE Mineral Display Specimen S704

AU $14.99 (0 Bids)
End Date: Sunday Dec-17-2017 23:06:20 EST
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183.5ct/36.5g Chalcedony Stalactites w/ Pink Stilbite Mineral Specimen - CS307

AU $14.99 (0 Bids)
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157.5ct/31.5g Stilbite Chalcedony Apophyllite Mineral Display Specimen ASC237

AU $9.99 (0 Bids)
End Date: Sunday Dec-17-2017 23:04:19 EST
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423.5ct/84.5g Chalcedony Stilbite Mordenite Geode Mineral Display Specimen CS336

AU $12.99 (0 Bids)
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39g Clear Apophyllite on Blue Chalcedony Crystal Mineral Specimen Zeolite AC439

AU $9.99 (0 Bids)
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52.5g Green Apophyllite Cube on Chalcedony Mineral Specimen Zeolite India AC437

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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272g 62MM MADAGASCAR NATURAL LIGHT GREEN OPAL JASPER CRYSTAL SPHERE BALL

AU $26.00 (18 Bids)
End Date: Tuesday Dec-12-2017 17:56:29 EST
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Beautiful Triangular Self Healed Angel Opal Quartz Crystal Cluster

AU $48.00
End Date: Tuesday Dec-19-2017 21:51:44 EST
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#CC9. ROCK WITH OPAL STREAKS

AU $50.00
End Date: Saturday Dec-16-2017 13:48:51 EST
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Yowah Nut Material Australian Boulder Opal Unpolished Gemstone Specimen RP914

AU $214.50
End Date: Monday Dec-25-2017 12:18:22 EST
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Boulder opal mineral specimen collection lapidary skin polishing carving MI08

AU $150.00
End Date: Wednesday Dec-20-2017 16:01:15 EST
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Beautiful West Australian green opal with magnesite mineral slab with stand

AU $105.00
End Date: Saturday Dec-30-2017 16:23:04 EST
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