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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Large Quartz Crystal Plate

AU $35.00
End Date: Friday Jun-23-2017 15:25:30 EST
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White quartz cave 2.137kg

AU $70.00
End Date: Thursday Jun-22-2017 21:49:36 EST
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Mooralla Smokey Quartz Geode with Smokeys!

AU $40.00
End Date: Tuesday Jun-20-2017 15:24:33 EST
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Mooralla Smokey Quartz Geode with Smokeys!

AU $25.00
End Date: Tuesday Jun-20-2017 15:22:44 EST
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*50% OFF SALE!* Mooralla Smokey Quartz Geode with Smokeys!

AU $14.99
End Date: Tuesday Jun-20-2017 15:20:34 EST
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Mooralla Smokey Quartz Geode with Smokeys!

AU $110.00
End Date: Monday Jun-19-2017 23:39:50 EST
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Clear Quartz Crystal from Madagascar.

AU $19.99
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Some of the common varieties of chalcedony are:

   

Chalcedony specimens now available (at eBay):

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79.30gr 100% Natural Purple Botryoidal Chalcedony Grape Agate

AU $35.00 (0 Bids)
End Date: Wednesday May-31-2017 17:00:42 EST
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352ct/70.5g White Chalcedony Crystal Mineral Display Specimen Zeolite - C516

AU $14.99 (0 Bids)
End Date: Tuesday May-30-2017 18:15:51 EST
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115ct/23g Sugary White Chalcedony Mineral Display Specimen Zeolite - C515

AU $9.99 (0 Bids)
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Chalcedony - Arkaroola, SA

AU $4.00 (0 Bids)
End Date: Monday May-29-2017 20:38:12 EST
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168.5ct/34g Pink Scolecite & Chalcedony Mineral Display Specimen Zeolite SE7021

AU $16.99 (0 Bids)
End Date: Sunday May-28-2017 19:37:50 EST
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129g Pink Stilbite on White Chalcedony Mineral Specimen Zeolite India CS314

AU $16.99 (0 Bids)
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Chalcedony , Dendritic - Angaston, SA

AU $2.00 (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 Faceted Oval Ethiopian Welo Opal Silver Earrings - lapidary, jewelry

AU $32.00
End Date: Friday Jun-23-2017 20:22:08 EST
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Large Boulder opal mineral specimen collection lapidary - BO17

AU $160.00
End Date: Tuesday Jun-20-2017 14:44:44 EST
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Red & Green Opal Fossil 200 grams

AU $8,500.00
End Date: Monday Jun-19-2017 16:16:19 EST
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Large white/blue raw/natural opal specimen 497 grams

AU $620.00 (0 Bids)
End Date: Saturday May-27-2017 14:54:02 EST
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Rough Opal / Black Opal Soft Rubbed #77

AU $180.00
End Date: Monday Jun-19-2017 14:20:00 EST
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Rough Opal 34.75ct #20

AU $200.00
End Date: Monday Jun-19-2017 14:17:08 EST
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Yowah Nut Material Australian Boulder Opal Unpolished Gemstone Specimen RP914

AU $195.00 (0 Bids)
End Date: Saturday May-27-2017 7:40:32 EST
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