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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6pc NATURAL CRYSTAL POLISHED POINTS LOT - CITRINE FLUORITE QUARTZ AGATE 226g

AU $28.99
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82mm RARE FORMED WINDOW TWIN TERMINATION natural SMOKY QUARTZ CRYSTAL POINT

AU $16.99
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RARE AAA EXOTIC RUTILE HAIRS INCLUDED QUARTZ polished CRYSTAL POINT nat rough

AU $13.99
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RARE AAA EXOTIC RUTILE HAIRS INCLUDED QUARTZ polished CRYSTAL POINT nat rough

AU $16.99
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RARE AAA EXOTIC RUTILE HAIRS INCLUDED QUARTZ polished CRYSTAL POINT nat rough

AU $14.99
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41g EXOTIC RUTILE HAIRS INCLUDED QUARTZ polished FACETED CRYSTAL POINT nat rough

AU $17.99
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Some of the common varieties of chalcedony are:

   

Chalcedony specimens now available (at eBay):

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36g Pink Stilbite on Blue/Grey Chalcedony Mineral Specimen Zeolite CS334

AU $9.99 (0 Bids)
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28.5g Pink Stilbite on Grey Chalcedony Mineral Specimen Zeolite CS340

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232.5g Pink Stilbite on White Chalcedony Mineral Specimen Zeolite India CS341

AU $24.99 (0 Bids)
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11g Blue Chalcedony w/ Mordenite Stalactite Mineral Specimen Zeolite India C517

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Chalcedony "stalactite" Nasik Maharashtra India

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115ct/23g Sugary White Chalcedony Mineral Display Specimen Zeolite - C515

AU $9.99 (0 Bids)
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54ct/11g Small White Chalcedony Stalactites Mineral Display Specimen Zeolite

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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 Natural Opal Matrix Rough Specimen

AU $50.00 (1 Bid)
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Andamooka Natural Hard Opal Matrix Rough Specimen

AU $50.00 (1 Bid)
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Approx 40CT AUSTRALIAN BOULDER OPAL CHIPS ROUGH OPAL In GLASS BOTTLE 1129B

AU $9.50 (0 Bids)
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Gorgeous Australian Opal CARVED PENGUIN With Color (#L4353)

AU $49.95
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Queensland Boulder Opal Specimen

AU $65.00 (0 Bids)
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Scarce Andamooka Electric Blue Fluorescent Opal Phenomenon

AU $50.00 (1 Bid)
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