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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1.05lb Natural Clear White Obelisk Quartz Crystal point Healing 2-24-18

AU $9.99 (0 Bids)
End Date: Saturday Mar-4-2017 23:43:48 EST
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1.25lb Natural Clear White Obelisk Quartz Crystal point Healing 2-24-16

AU $19.99 (0 Bids)
End Date: Saturday Mar-4-2017 23:39:28 EST
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0.96lb Natural Clear White Obelisk Quartz Crystal point Healing 2-24-14

AU $19.99 (0 Bids)
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0.8lb Natural Clear White Obelisk Quartz Crystal point Healing 2-24-12

AU $19.99 (0 Bids)
End Date: Saturday Mar-4-2017 23:22:54 EST
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0.9lb Natural Clear White Obelisk Quartz Crystal point Healing 2-24-10

AU $19.99 (0 Bids)
End Date: Saturday Mar-4-2017 23:18:46 EST
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Barite on Quartz....China....105g

AU $95.00
End Date: Monday Mar-27-2017 15:46:33 EST
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QUARTZ CRYSTAL CLUSTER INVERELL NEW SOUTH WALES AUSTRALIA

AU $20.00
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Some of the common varieties of chalcedony are:

   

Chalcedony specimens now available (at eBay):

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

AU $14.99 (0 Bids)
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Chalcedony Slab Western Australia

AU $10.00 (0 Bids)
End Date: Tuesday Mar-7-2017 17:05:48 EST
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Citron Chrysoprase with Chalcedony Rough specimen Western Australia

AU $10.00 (0 Bids)
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Chalcedony Slab From Western Australia

AU $22.00
End Date: Sunday Mar-26-2017 20:04:49 EST
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Chalcedony Slab From Western Australia

AU $10.00
End Date: Sunday Mar-26-2017 20:02:12 EST
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436ct/87g Pink STILBITE on Boytroidal CHALCEDONY Mineral Display Specimen CS310

AU $16.99 (0 Bids)
End Date: Thursday Mar-2-2017 19:37:58 EST
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115ct/23g Sugary White Chalcedony Mineral Display Specimen Zeolite - C515

AU $9.99 (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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Treated Andamooka matrix opal (Fairy opal)

AU $120.00
End Date: Tuesday Mar-7-2017 13:01:10 EST
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Rough Opal / Semi Black Opal Soft Rub 4.6ct #94

AU $46.00
End Date: Friday Mar-24-2017 22:45:50 EST
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From Oz VERY RARE Beautiful Opal Specimen from Vintage Rock & Fossil Collection

AU $199.95
End Date: Saturday Mar-4-2017 14:46:03 EST
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Boulder opal mineral specimen collection lapidary skin polishing car

AU $70.00
End Date: Thursday Mar-23-2017 7:10:58 EST
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Boulder opal mineral specimen collection lapidary skin polishing carving - BO15

AU $45.00
End Date: Thursday Mar-23-2017 6:52:47 EST
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Rough Opal 14.37ct #62

AU $5.85 (0 Bids)
End Date: Monday Feb-27-2017 15:37:06 EST
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ANDAMOOKA OPAL ROUGH 10 GRAMS (50CTS) A40 SINGLE STONE NOT PARCEL

AU $20.00
End Date: Tuesday Mar-21-2017 18:33:57 EST
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