opal

Name:

opal

A photo of the mineral opal

Class:

Silicates

Chemistry:

SiO2 * nH2O Hydrated Silica

Color(s):

colorless, red, green, blue, brown, black, milky, yellow etc. "precious opal" is distinguished by "color-play" or "fire"

Hardness:

5.5 - 6.5

SpecGrav:

1.0 - 2.5

Fracture:

conchoidal

Cleavage:

none

Crystal:

amorphous (a layered silica formed in a precipitation process and cemented with a hydrous silica cement)

Envronment:

precipitation process, or "fossilization product" as in the replacement of organic materials (opalized wood, clam, shell, etc.)

Association:

zeolites, limonite, chalcedony

Locals:

| Austrailia | Brazil | Nevada,Wyoming,Montana, USA | Tanzania | Iceland | Mexico |

Misc:

Opal may go by a number of names depending on the kind, some examples include hyalite (clear transparent samples 1-3 below), Cloudy or Milky (samples 4-6), clear or slightly cloudy (samples 7-9), fossilized opal (samples 10-11), sand stone opal (samples 12-14), Mexican opal (15), fire opal (16), green prose opal, brown liver opal ... It is easily damaged by dehydration thermally or chemically. Heat can dehydrate and crack opal, and solvents with an affinity for water can damage opal (acetone, strong bases, some acids). Soluble in KOH solutions.

Photos
& Locals:

1.) Squaretop Mtn., Queensland, Austrailia VAR: Hyalite
2.) Squaretop Mtn., Queensland, Austrailia VAR: Hyalite
3.) Squaretop Mtn., Queensland, Austrailia VAR: Hyalite
4.) Austrailia VAR: White (w/color)
5.) Austrailia VAR: White (w/color)
6.) Austrailia VAR: White (w/color)
7.) Brazil VAR: clear (w/color)
8.) Brazil VAR: clear (w/color)
9.) Brazil VAR: clear (w/color)

10.) Nevada VAR: tree limb cast
11.) Nevada VAR: tree limb cast
12.) Hondourus VAR: opalitic sandstone
13.) Louisiana VAR: opalitic conglomerate
14.) Louisiana VAR: opalitic conglomerate
15.) Austrailia VAR: opal in Limonite base
16.) Austrailia VAR: opal in Limonite base
17.) Mexican VAR: opal rhyolite
18.) Mexican VAR: opal in rhyolite ... var:(fire opal)

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Name:	opal
Class:	Silicates
Chemistry:	SiO2 * nH2O Hydrated Silica
Color(s):	colorless, red, green, blue, brown, black, milky, yellow etc. "precious opal" is distinguished by "color-play" or "fire"
Hardness:	5.5 - 6.5	SpecGrav:	1.0 - 2.5
Fracture:	conchoidal	Cleavage:	none
Crystal:	amorphous (a layered silica formed in a precipitation process and cemented with a hydrous silica cement)
Envronment:	precipitation process, or "fossilization product" as in the replacement of organic materials (opalized wood, clam, shell, etc.)
Association:	zeolites, limonite, chalcedony
Locals:	\| Austrailia \| Brazil \| Nevada,Wyoming,Montana, USA \| Tanzania \| Iceland \| Mexico \|
Misc:	Opal may go by a number of names depending on the kind, some examples include hyalite (clear transparent samples 1-3 below), Cloudy or Milky (samples 4-6), clear or slightly cloudy (samples 7-9), fossilized opal (samples 10-11), sand stone opal (samples 12-14), Mexican opal (15), fire opal (16), green prose opal, brown liver opal ... It is easily damaged by dehydration thermally or chemically. Heat can dehydrate and crack opal, and solvents with an affinity for water can damage opal (acetone, strong bases, some acids). Soluble in KOH solutions.

	Photos & Locals:
		1.) Squaretop Mtn., Queensland, Austrailia VAR: Hyalite 2.) Squaretop Mtn., Queensland, Austrailia VAR: Hyalite 3.) Squaretop Mtn., Queensland, Austrailia VAR: Hyalite 4.) Austrailia VAR: White (w/color) 5.) Austrailia VAR: White (w/color) 6.) Austrailia VAR: White (w/color) 7.) Brazil VAR: clear (w/color) 8.) Brazil VAR: clear (w/color) 9.) Brazil VAR: clear (w/color)		10.) Nevada VAR: tree limb cast 11.) Nevada VAR: tree limb cast 12.) Hondourus VAR: opalitic sandstone 13.) Louisiana VAR: opalitic conglomerate 14.) Louisiana VAR: opalitic conglomerate 15.) Austrailia VAR: opal in Limonite base 16.) Austrailia VAR: opal in Limonite base 17.) Mexican VAR: opal rhyolite 18.) Mexican VAR: opal in rhyolite ... var:(fire opal)

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