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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Quartz - Var: Smoky Mooralla Victoria

AU $35.00 (0 Bids)
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Scheelite on Quartz Yaogangxian Mine Chenzou Hunan Province China

AU $20.00 (2 Bids)
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"Hot Springs" Quartz crystals Mt. Ida Arkansas U.S.A.

AU $25.00 (0 Bids)
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Cognac Natural Citrine Quartz Point from Brazil 3-4 grams each x1

AU $6.95
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50mm NATURAL PINK LEMURIAN SEED natural TERMINATED QUARTZ CRYSTAL POINT

AU $6.99
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2pc NATURAL CLEAR / SMOKY QUARTZ DOUBLE TERMINATED dt QUARTZ CRYSTAL POINTS

AU $9.49
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23g TANGERINE AURA QUARTZ natural TERMINATED CRYSTAL POINT

AU $9.99
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Some of the common varieties of chalcedony are:

   

Chalcedony specimens now available (at eBay):

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GRAPE CHALCEDONY botryoidal specimen 25,8g - 5,1 x 3,2 x 2,3 cm INDONESIA Mamuju

AU $64.06
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314ct/63g Milky STILBITE CHALCEDONY & SCOLECITE Mineral Display Specimen S704

AU $12.99 (0 Bids)
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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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Chalcedony "stalactite" Nasik Maharashtra India

AU $45.00 (0 Bids)
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Chalcedony & Stilbite Stalactite Specimen Museum Grade

AU $165.00
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LOT OF 8 AGATE AND CHALCEDONY SPECIMENS 372 G

AU $12.00
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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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Large Andamooka Painted Lady Opal Specimen

AU $700.00
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Australian Boulder Opal “Grounding Stone and Helps Overcomes Negative Energy”

AU $195.00
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Scarce Andamooka Electric Blue Fluorescent Polished Opal

AU $50.00 (0 Bids)
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Andamooka Rough Opal Parcel

AU $50.00 (0 Bids)
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Crystal Pipe Opal. Opal Rough. Opal Fossil. Australian Opal. Natural Opal. Gem

AU $80.00 (0 Bids)
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2pc BLUISH HUE WHITE OPAL 11X9mm POLISHED OVAL CUT LOOSE CABOCHONS nat rough

AU $8.99
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2pc BLUISH HUE WHITE OPAL 11X9mm POLISHED OVAL CUT LOOSE CABOCHONS nat rough

AU $8.49
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