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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60mm GOLDEN CITRINE NATURAL TERMINATED QUARTZ CRYSTAL - BRAZIL MINED

AU $7.99
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2x Candle/Pineapple Quartz Crystals, Copeton NSW Australia. Nice Pieces

AU $4.99 (0 Bids)
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Quartz Crystals clear/smokey bulk lot x18, Tingha NSW Australia

AU $3.99
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EPIDOTE crystals on Quartz - Pampa Bianca District , Peru - 2.4x2.2x1.3cm NICE!

AU $8.90
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Quartz Rock Crystal bulk lot x10, Howell NSW Australia

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Some of the common varieties of chalcedony are:

   

Chalcedony specimens now available (at eBay):

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11g Blue Chalcedony w/ Mordenite Stalactite Mineral Specimen Zeolite India C517

AU $9.99 (0 Bids)
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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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36g Pink Stilbite on Blue/Grey Chalcedony Mineral Specimen Zeolite CS334

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28.5g Pink Stilbite on Grey Chalcedony Mineral Specimen Zeolite CS340

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

AU $9.99 (0 Bids)
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314ct/63g Milky STILBITE CHALCEDONY & SCOLECITE Mineral Display Specimen S704

AU $12.99 (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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Queensland Boulder Opal Specimen

AU $65.00 (0 Bids)
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RAW BOULDER OPAL 42 X 31 X 27 MM 57 G

AU $14.00
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DENDRITIC OPAL SPECIMEN PROMOTING SPIRITUAL GROWTH 116 X 94 X 87 MM 760 G

AU $36.00
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Two Andamooka Natural Untreated Opal Matrix Rough Specimens

AU $50.00 (0 Bids)
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Andamooka Treated Opal Matrix Rough - 4 Specimens

AU $50.00 (0 Bids)
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RAW WHITE COMMON OPAL WITH MINOR DENDRITES 100 X 60 X 44 MM 307 G

AU $34.00
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Mexican Fire Opal

AU $50.00
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