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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Clear QUARTZ crystal - Diamantina, Minas Gerais, Brazil - 5.5x1.5cm 10.7g NICE

AU $9.00
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Clear QUARTZ crystal - Diamantina, Minas Gerais, Brazil - 4.6x1.8cm 13.3g NICE

AU $9.00
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QUARTZ cluster - Corinto, Minas Gerais, Brazil - 5x4x3cm NICE

AU $25.00
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QUARTZ cluster - Corinto, Minas Gerais, Brazil - 4.2x3.5x2.5cm NICE

AU $22.00
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QUARTZ cluster - Corinto, Minas Gerais, Brazil - 4.5x4x3cm NICE

AU $22.00
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Mineral China Quartz and Pyrite with Aragonite cluster mineral specimen

AU $10.00 (0 Bids)
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Some of the common varieties of chalcedony are:

   

Chalcedony specimens now available (at eBay):

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Chalcedony , Dendritic - Angaston, SA

AU $2.00
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54ct/11g Small White Chalcedony Stalactites Mineral Display Specimen Zeolite

AU $10.99
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59 mm BIZARRE AGATE/CHALCEDONY NODULE FROM MOROCCO

AU $10.00 (0 Bids)
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LOT 100 cts CHALCEDONY NATURAL (stones precious/ fine)

AU $264.61
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45g Clear Apophyllite Cubes on Chalcedony Mineral Specimen Zeolite India AC429

AU $9.99
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Bigstargarstone BLUE CHALCEDONY MINERALS FORM INDIA

AU $2.99 (0 Bids)
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Bigstargarstone CHALCEDONY BALLS ON CHOCLATI STILBITE MINERALS

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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 $30.00
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From Oz VERY RARE Beautiful Opal Specimen from Vintage Rock & Fossil Collection

AU $199.95
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OPALS [Ward] Black + Boulder + Light Opal, Crystals, Fossils, Mexican 1stEd 1997

AU $28.25
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Rough Opal / Black Opal Soft Rubbed #77

AU $180.00
End Date: Wednesday Jul-19-2017 14:20:22 EST
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69.79 GRAMS (348.95CT) FAIRY OPAL ROUGH (TREATED BOULDER MATRIX) NOT PARCEL F6

AU $87.23
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27.65 GRAMS (138.25CT) FAIRY OPAL ROUGH (TREATED BOULDER MATRIX) NOT PARCEL F5

AU $20.73
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63.46 GRAMS (317.3 CT) FAIRY OPAL ROUGH (TREATED BOULDER MATRIX) NOT PARCEL F2

AU $79.33
End Date: Tuesday Jul-18-2017 19:26:54 EST
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