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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Calcite on Quartz Jalgaon district Maharashtra State India

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Ilvaite with Calcite & Quartz Second Soviet Mine Dal'negorsk Russia

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Quartz Rock Crystal bulk lot x10, Copeton NSW Australia (L212)

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Very large Stilbite crystals on Quartz Nashik Maharashtra India

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Apophyllite with Stilbite on Quartz Jalgaon Maharashtra India

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Apophyllite crystals with Quartz Jalgaon Maharashtra India

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Apophyllite with Quartz Jalgaon district Maharashtra State India

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Some of the common varieties of chalcedony are:

   

Chalcedony specimens now available (at eBay):

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NATURAL CHALCEDONY DRUZY FOSSILIZED SHELL PENDANT BEAD RAREST NEW MATERIAL 1.5"

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314ct/63g Milky STILBITE CHALCEDONY & SCOLECITE Mineral Display Specimen S704

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

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

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352ct/70.5g White Chalcedony Crystal Mineral Display Specimen Zeolite - C516

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Calcite with Chalcedony overgrowths Nashik Maharashtra State India

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AUSTRALIAN OPALITE Mini Slab with Druzy Covered Orange Chalcedony Lapidary

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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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Queensland Boulder Opal Specimen

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BOULDER OPAL 89 Х 66 X 35 MM 138 G

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Andamooka Treated Matrix Opal Specimens (2) 30 16 05 20

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Andamooka Treated Matrix Opal Specimen 31 16 05 20

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Andamooka Crystal Opal Specimen 25 16 05 20

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Andamooka Matrix Opal Specimen 20 16 05 20

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Andamooka Treated Matrix Opal Specimen 19 16 05 20

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