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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Mooralla quartz crystal

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147mm LONG HIGH QUALITY NATURAL CLEAR QUARTZ EARTH MINED WAND POINT

AU $29.49
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1000G TERMINATED CLEAR QUARTZ natural EARTH MINED CRYSTALS 1 kg BULK LOT

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Himalayan Chlorite Quartz Crystal, Ganesh Himal, Nepal.

AU $49.99
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3pc NATURAL BLUE AQUAMARINE / ROSE QUARTZ / GOLD CITRINE rough NATURAL CRYSTALS

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DUMORTERITE in QUARTZ - Bahia, Brazil - 5.5x4x3.5cm 95g Rare and Nice!

AU $50.00
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45mm NATURAL CLEAR QUARTZ CRYSTAL polished CRYSTAL STANDING POINT

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Some of the common varieties of chalcedony are:

   

Chalcedony specimens now available (at eBay):

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54ct/11g Small White Chalcedony Stalactites Mineral Display Specimen Zeolite

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

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183.5ct/36.5g Chalcedony Stalactites w/ Pink Stilbite Mineral Specimen - CS307

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

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

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10g Stilbite Scolecite on Chalcedony Stalactite Mineral Specimen Zeolite SE7041

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157.5ct/31.5g Stilbite Chalcedony Apophyllite Mineral Display Specimen ASC237

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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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Australian Boulder Opal Specimen (35mm) opal 703

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Treasures Of The Earth Gemstones X20 With BONUS. Ruby Emerald Sapphire Opal

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908g 91MM MADAGASCAR NATURAL LIGHT GREEN OPAL JASPER CRYSTAL SPHERE BALL HEALING

AU $240.00
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Fire Opal Cabochon Drops Healing Stone, Magic approx. 23x15x8MM 3,1g

AU $127.60
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Beautiful Triangular Self Healed Angel Opal Quartz Crystal Cluster

AU $40.00
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Opal pitchstone. 771.7 ct. Saint-Pierre-Eynac, Haute-Loire, France Ultra rare

AU $124.72
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Beautiful COOBER PEDY [Opal Capital of the World] intact perf'd 4 postcard sheet

AU $19.95
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