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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Semi Polished - Grape AGATE Chalcedony Quartz - Indonesia - Unique! 22g NICE

AU $14.90
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QUARTZ cluster - Corinto, Minas Gerais, Brazil - 4.5x4x3cm NICE

AU $22.00
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Semi Polished - Grape AGATE Chalcedony Quartz - Indonesia 3.5x1x1.6cm NICE

AU $6.90
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Semi Polished - Grape AGATE Chalcedony Quartz - Indonesia 3.5x2.1x1.7cm NICE

AU $10.90
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Semi Polished - Grape AGATE Chalcedony Quartz - Indonesia -3.8x2x2.1cm NICE

AU $14.90
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Semi Polished - Grape AGATE Chalcedony Quartz - Indonesia 4.5x2.5x2.2cm NICE

AU $14.90
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Some of the common varieties of chalcedony are:

   

Chalcedony specimens now available (at eBay):

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Natural Brown Chalcedony Coral Minerals Specimen

AU $3.00 (0 Bids)
End Date: Monday Apr-29-2019 23:17:26 EST
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Natural Chalcedony Coral Minerals Specimen ( 18X12)

AU $120.00 (0 Bids)
End Date: Thursday May-2-2019 23:17:19 EST
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Natural Apophyllite Crystals On Chalcedony Coralminerals Specimen

AU $12.50 (0 Bids)
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Pointed Apophyllite Crystals On Blue Chalcedony Coral Minerals Specimen

AU $9.99 (0 Bids)
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Natural Apophyllite Crystals On Chalcedony Staltactite Minerals

AU $30.00 (0 Bids)
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Natural Apophyllite Crystals On Chalcedony Coral 10 Nos Minerals Specimen

AU $100.00 (0 Bids)
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Red Stilbite On Matrix Chalcedony Minerals Specimen

AU $5.88 (0 Bids)
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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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(Lot 222)Boulder Opal stone with multi colours for pendant or braclet.

AU $150.00 (0 Bids)
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CACHOLONG OPAL VARIETY COMMON OPAL109 X 81 X 53 MM 550 G

AU $34.00 (0 Bids)
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Beautiful Chunky Andamooka Matrix Opal Slab

AU $50.00 (1 Bid)
End Date: Monday Apr-29-2019 18:52:21 EST
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Andamooka Acid Treated Opal Matrix Rough Specimen

AU $50.00 (0 Bids)
End Date: Friday Apr-26-2019 18:36:52 EST
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Scarce Andamooka Opal Matrix Rough Slab

AU $50.00 (0 Bids)
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Andamooka Opal Matrix Rough Specimen

AU $50.00 (0 Bids)
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Fat Untreated Andamooka Opal Matrix Slab

AU $50.00 (0 Bids)
End Date: Thursday Apr-25-2019 17:37:59 EST
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