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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Candle Pineapple Quartz Crystal Specimen, Copeton NSW

AU $5.99 (0 Bids)
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116g BRAZIL LEMURIAN SMOKY QUARTZ - EARTH MINED CRYSTAL

AU $18.99
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87mm YELLOW QUARTZ NATURAL TERMINATED CRYSTAL WAND POINT

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5pc RARE UNIQUE FORMED SMOKY QUARTZ rough DOUBLE TERMINATED dt CRYSTAL LOT

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100g NATURAL MIXED COLOR RAW QUARTZ rough AMETHYST CLEAR SMOKY BULK LOTS

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Quartz Crystal Cluster Sichuan Province, China (EA6657) mineral reiki healing

AU $50.00
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37mm TWIN TERMINATED SUPER CLEAR QUARTZ natural EARTH MINED CRYSTAL

AU $9.49
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Some of the common varieties of chalcedony are:

   

Chalcedony specimens now available (at eBay):

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

AU $9.99 (0 Bids)
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115ct/23g Sugary White Chalcedony Mineral Display Specimen Zeolite - C515

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

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183.5ct/36.5g Chalcedony Stalactites w/ Pink Stilbite Mineral Specimen - CS307

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28.5g Pink Stilbite on Grey Chalcedony Mineral Specimen Zeolite CS340

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

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

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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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Australia opal Specimen Rock Fossil

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28ct Coarse grained Andamooka Matrix Opal Specimen.  

AU $30.00 (0 Bids)
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80 grams Andamooka Matrix Opal Specimen

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101ct Andamooka Matrix Opal Specimen

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30ct Andamooka Matrix Opal Specimen

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30ct Andamooka Matrix Opal Specimen.

AU $55.00 (0 Bids)
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Andamooka Fluorescent Blue Tumbled Polished Opal

AU $50.00 (0 Bids)
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