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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Quartz Crystal bulk lot x10, Tingha NSW Australia

AU $7.49 (0 Bids)
End Date: Monday Jun-8-2020 10:59:14 EST
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Tourmaline in Clear Quartz Crystal, NSW Australia (Tourmalinated Rutilated)

AU $7.99
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Quartz Crystal bulk lot x10, Copeton NSW Australia (L77)

AU $4.50 (0 Bids)
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Smokey Quartz cluster, Elsmore NSW Australia

AU $5.99 (0 Bids)
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Schorl Tourmaline Blue Quartz Crystals Tasmania Australia (EA8733)

AU $42.00
End Date: Wednesday Jun-24-2020 14:43:02 EST
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Nice Smokey Quartz Crystal, Elsmore NSW Australia

AU $19.99
End Date: Tuesday Jun-23-2020 15:29:52 EST
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Aussie MOLYBDENITE crystal on Quartz, Kingsgate, NSW, Australia Molybdenum NICE

AU $58.00
End Date: Sunday Jun-21-2020 11:13:16 EST
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Some of the common varieties of chalcedony are:

   

Chalcedony specimens now available (at eBay):

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11g Blue Chalcedony w/ Mordenite Stalactite Mineral Specimen Zeol

AU $9.99 (0 Bids)
End Date: Monday Jun-8-2020 18:29:15 EST
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28.5g Pink Stilbite on Grey Chalcedony Mineral Specimen Zeolite CS340

AU $9.99 (0 Bids)
End Date: Monday Jun-8-2020 18:28:26 EST
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232.5g Pink Stilbite on White Chalcedony Mineral Specimen Zeolite India CS341

AU $24.99 (0 Bids)
End Date: Monday Jun-8-2020 18:28:14 EST
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36g Pink Stilbite on Blue/Grey Chalcedony Mineral Specimen Zeolite CS334

AU $9.99 (0 Bids)
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148.5ct/30g Chalcedony Stalactite w/ Apophyllite Mineral Display Specimen AC401

AU $12.99 (0 Bids)
End Date: Tuesday Jun-2-2020 17:17:33 EST
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63.5ct/12.5g Grey Chalcedony Stalactite Crystal Mineral Display Specimen C501

AU $9.99 (0 Bids)
End Date: Tuesday Jun-2-2020 17:17:33 EST
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108.5ct/22g Grey Chalcedony w/ Stilbite Crystal Mineral Display Specimen CS301

AU $12.99 (0 Bids)
End Date: Sunday Jun-7-2020 19:55:10 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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Andamooka Treated Opal Matrix Rough Specimen 13 24 04 20

AU $45.00 (0 Bids)
End Date: Thursday Jun-11-2020 16:41:24 EST
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Crystal Opal Smalls 02 24 04 20

AU $45.00 (0 Bids)
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Andamooka Treated Matrix Opal Specimens 09 24 04 20

AU $45.00 (0 Bids)
End Date: Thursday Jun-11-2020 16:24:55 EST
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Opal Rough Chips All Pieces Have Color

AU $45.00 (0 Bids)
End Date: Thursday Jun-11-2020 16:23:09 EST
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Andamooka Treated Matrix Opal 05 24 04 20

AU $50.00 (0 Bids)
End Date: Thursday Jun-11-2020 16:00:35 EST
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Opal Hexagonal Crab Shape 17 24 04 20

AU $45.00 (0 Bids)
End Date: Thursday Jun-11-2020 15:52:09 EST
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Opal Hexagonal Shapes

AU $45.00 (0 Bids)
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