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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533ct/106.5g Green Rutilated Phantom Quartz Healing Crystal Mineral Specimen Q66

AU $19.99
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645ct/129g Black Schorl Tourmaline w Quartz Mineral Display Specimen T152

AU $24.99
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144g PINK ROSE QUARTZ CRYSTAL SKULL polished HAND CARVED ART

AU $34.99
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HAND CARVED EXOTIC HUMMINGBIRD on AMETHYST CLUSTER sodalite rose quartz

AU $37.99
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70mm YELLOW LEMURIAN QUARTZ dt DOUBLE TERMINATED CRYSTAL POINT

AU $9.99
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50g EXOTIC MIXED COLOR natural RAW QUARTZ CRYSTAL LOT

AU $10.99
End Date: Saturday Apr-29-2017 9:42:09 EST
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49.5ct/10g Tibetan Twin Quartz Mineral Display Specimen Crystal Point Q73

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

AU $14.99 (0 Bids)
End Date: Thursday Apr-6-2017 17:55:24 EST
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143.5ct/28.5g Orange Scolecite w Chalcedony Mineral Display Specimen SE7038

AU $18.99
End Date: Saturday Apr-29-2017 17:40:43 EST
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79.30gr 100% Natural Purple Botryoidal Chalcedony Grape Agate

AU $35.00 (0 Bids)
End Date: Wednesday Apr-5-2017 14:51:53 EST
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63.5ct/12.5g Grey Chalcedony Stalactite Crystal Mineral Display Specimen C501

AU $9.99 (0 Bids)
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45g Clear Apophyllite Cubes on Chalcedony Mineral Specimen Zeolite India AC429

AU $9.99 (0 Bids)
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54ct/11g Small White Chalcedony Stalactites Mineral Display Specimen Zeolite

AU $10.99
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Chalcedony Natural On Matrix

AU $6.00 (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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BOULDER OPAL ROUGH 27 GRAMS (135CTS) B113 SINGLE STONE NOT PARCEL

AU $5.00
End Date: Saturday Apr-29-2017 22:31:36 EST
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BOULDER OPAL ROUGH 32 GRAMS (160CTS) B117 SINGLE STONE NOT PARCEL

AU $5.00
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BOULDER OPAL ROUGH 2.1 GRAMS (10.5CTS) B159 SINGLE STONE NOT PARCEL

AU $14.99
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BOULDER OPAL ROUGH 5.31 GRAMS (26.55CTS) B341 SINGLE STONE NOT PARCEL

AU $10.00
End Date: Wednesday Apr-26-2017 20:31:16 EST
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BOULDER OPAL ROUGH 11.24 GRAMS (56.2CTS) B334 SINGLE STONE NOT PARCEL

AU $10.00
End Date: Wednesday Apr-26-2017 20:09:00 EST
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BOULDER OPAL ROUGH 15.09 GRAMS (75.45CTS) B333 SINGLE STONE NOT PARCEL

AU $10.00
End Date: Wednesday Apr-26-2017 20:06:39 EST
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BOULDER OPAL ROUGH 10.78 GRAMS (53.9CTS) B331 SINGLE STONE NOT PARCEL

AU $10.00
End Date: Wednesday Apr-26-2017 20:00:15 EST
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