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Post by Pat on Jun 22, 2012 17:42:40 GMT -5
???I have a chunk of translucent purple something with a couple of bubbles. Is there a way to tell the difference between obsidian and industrial slag glass? I've heard that bubbles don't occur in obsidian. Are there any other indications? Thanks.
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Post by jakesrocks on Jun 22, 2012 17:55:05 GMT -5
If it has bubbles, it's glass.
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Post by 3rdrockfromthefun on Jun 22, 2012 18:34:25 GMT -5
Bubbles occur in obsidian too - this is a really good question. Okay, so - if my mass spectrometer is down  how do I tell the difference when it comes to glass that looks a lot like obsidian? Does obsidian fall within an sg range that glass generally does not? Is obsidian conductive in the least relative to glass (it does have a lot of iron it it - I have one piece of sheen that is magnetic) - ? Thanks. |
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Post by FrogAndBearCreations on Jun 22, 2012 18:56:29 GMT -5
I have never seen any translucent or clear obsidian of color, only browns and grays that were clear
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Post by 3rdrockfromthefun on Jun 22, 2012 22:39:45 GMT -5
The batch before last of obsidian I ordered from hand-2-mouth mining was very translucent (Davis Creek - "Autumn Sunset" was the color I think) and very colorful - in fact I'd say 'extremely' colorful. Anyway, when thick even it's translucent and when thinned to about 1/4" I can see the color of my fingers through it.
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Post by helens on Jun 22, 2012 23:33:23 GMT -5
Post a pix, I can probably tell you from the color:P.
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Post by FrogAndBearCreations on Jun 23, 2012 9:13:53 GMT -5
yes that type of obsidian has "color" in it when viewed at the correct angle and light but its not a clear color like a hunk of glass would be. It goes black if the light is not at the right angle to the color bands. Its very directional in the way you need to cut it so that the color shows up and yes it can be translucent.
If you did not orient that cut correctly you would not have the neat color play across the face of the slab. It would show only on the sides and the face would be translucent dull black, or gray with way less color than the edges.
I state again that I have never seen glass clear brightly colored obsidian!
Only clear brown, gray clear apache tears obsidian and some of the clear flow obsidians with the flames of mahogany(ribbon obsidian)
there are some sellers on the bay selling green and purple glass as obsidian. Even the Mount St.Helens ash will not make a clear glass and they only put a little dab of it in the glass they are making so they can say it glass from the mount st helens ash.
Lots of gimicks out there that will lighten your wallet and tell you a lie!
there are obsidians that are deep purple, deep green and yellow that have translucents but they are VERY rare.
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Post by FrogAndBearCreations on Jun 23, 2012 9:55:36 GMT -5
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Post by jakesrocks on Jun 23, 2012 11:40:22 GMT -5
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Post by Pat on Jun 23, 2012 13:44:19 GMT -5
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Post by 3rdrockfromthefun on Jun 23, 2012 14:20:40 GMT -5
yes that type of obsidian has "color" in it when viewed at the correct angle and light but its not a clear color like a hunk of glass would be. It goes black if the light is not at the right angle to the color bands. Its very directional in the way you need to cut it so that the color shows up and yes it can be translucent. If you did not orient that cut correctly you would not have the neat color play across the face of the slab. It would show only on the sides and the face would be translucent dull black, or gray with way less color than the edges. I state again that I have never seen glass clear brightly colored obsidian! Only clear brown, gray clear apache tears obsidian and some of the clear flow obsidians with the flames of mahogany(ribbon obsidian) there are some sellers on the bay selling green and purple glass as obsidian. Even the Mount St.Helens ash will not make a clear glass and they only put a little dab of it in the glass they are making so they can say it glass from the mount st helens ash. Lots of gimicks out there that will lighten your wallet and tell you a lie! there are obsidians that are deep purple, deep green and yellow that have translucents but they are VERY rare. 5/8" thick Davis Creek Obsidian - in front of the light / Backlit (at any orientation) -   And behind the light / Frontlit -  When you say 'like glass' you're talking 'transparent', not 'translucent'. And at 1/4" thick this stuff get's MUCH clearer. Purchased from Hand-2-Mouth Mining - definitely no hoaxing going on here. While one could debate whether this were glass or obsidian (glass can be made chatoyant), if they did not know the source (reliable) but I've seen obsidian even more translucent than this and if one did not know if it were glass or obsidian it might be hard to tell - for me anyway. Additionally, I have seen glass less translucent than this (rock shop across town has some in their glass bin). Just putting my pictures where my mouth is... |
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Post by 3rdrockfromthefun on Jun 23, 2012 14:22:44 GMT -5
Pat - seeing you pictures that looks like glass to me.
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Post by Pat on Jun 23, 2012 14:43:43 GMT -5
Frank, why do you think it is glass? I don't care which it is, but I do want to know how to tell the difference.
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Post by 3rdrockfromthefun on Jun 23, 2012 15:07:06 GMT -5
Pat, because it's transparent, not translucent, for one - I can see the ruler quite clearly through it.
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Another reason is purely subjective - it looks like glass to me. That's one of the reason why I thought this was such a good question - it would be nice not to have to depend on an eye of experience to tell the difference - would rather have a checklist of facts
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Post by Pat on Jun 23, 2012 15:33:59 GMT -5
Sooo, is transparency the definitive answer? Looks like a maybe.
I would like to see that checklist...
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Post by helens on Jun 23, 2012 16:18:58 GMT -5
Hrm. That looks like light amethyst moretti glass (soft or 'soda-lime' glass) which is 104 COE. Moretti is the 'standard' type of utility and bead glass for hundreds of years (I work in borosilicate glass, which is 33 COE and a much tougher type of glass than soda-lime). I have that color soft glass. This is what it looks like as a tab: www.waleapparatus.com/catalog.asp?prodid=548474&showprevnext=1I think it should be noted that there's little difference chemically between obsidian and glass. Wiki for Obsidian: en.wikipedia.org/wiki/Obsidian"Obsidian is mineral-like, but not a true mineral because as a glass it is not crystalline....Obsidian consists mainly of SiO2 (silicon dioxide), usually 70% or more." Glass Wiki: en.wikipedia.org/wiki/Glass"The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica (SiO2) plus Na2O, CaO, and several minor additives. Silica (the chemical compound SiO2) is a common fundamental constituent of glass. In nature, vitrification of quartz occurs when lightning strikes sand, forming hollow, branching rootlike structures called fulgurite." Meteorites are the other form of natural glass. I think it's glass because it's transparent, not translucent. Also the color is so uniform... that white could be the edge of the crucible where the glass was made into rods for sale. The 'slag', or cullet, from the bottom and walls. But... people have a truly odd idea of value... that glass is 'cheap' and rocks are expensive. Um... Light amethyst glass costs $20 a lb retail. Wale Apparatus is a wholesaler to the trade and from them, it's $11.40 a lb, the $2.85 sale price is in 1/4 lb increments, as you can see from my link above. Rough obsidian costs way less than $20 a lb, or even $11/lb. Silvered glass costs up to $180 a lb. So if it's GLASS, it's worth MORE than solid obsidian rough (but not more than fancy 'rainbow' type obsidians). And I don't see why nature-made glass couldn't have bubbles, it's still glass:). |
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Post by FrogAndBearCreations on Jun 23, 2012 18:57:15 GMT -5
yes that type of obsidian has "color" in it when viewed at the correct angle and light but its not a clear color like a hunk of glass would be. It goes black if the light is not at the right angle to the color bands. Its very directional in the way you need to cut it so that the color shows up and yes it can be translucent. If you did not orient that cut correctly you would not have the neat color play across the face of the slab. It would show only on the sides and the face would be translucent dull black, or gray with way less color than the edges. I state again that I have never seen glass clear brightly colored obsidian! Only clear brown, gray clear apache tears obsidian and some of the clear flow obsidians with the flames of mahogany(ribbon obsidian) there are some sellers on the bay selling green and purple glass as obsidian. Even the Mount St.Helens ash will not make a clear glass and they only put a little dab of it in the glass they are making so they can say it glass from the mount st helens ash. Lots of gimicks out there that will lighten your wallet and tell you a lie! there are obsidians that are deep purple, deep green and yellow that have translucents but they are VERY rare. 5/8" thick Davis Creek Obsidian - in front of the light / Backlit (at any orientation) - And behind the light / Frontlit - When you say 'like glass' you're talking 'transparent', not 'translucent'. And at 1/4" thick this stuff get's MUCH clearer. Purchased from Hand-2-Mouth Mining - definitely no hoaxing going on here. While one could debate whether this were glass or obsidian (glass can be made chatoyant), if they did not know the source (reliable) but I've seen obsidian even more translucent than this and if one did not know if it were glass or obsidian it might be hard to tell - for me anyway. Additionally, I have seen glass less translucent than this (rock shop across town has some in their glass bin). Just putting my pictures where my mouth is... translucent/transparent colors ie. that purple glass not saying there is no translucent/clear obsidian yours is gray translucent and yes there is clear but with grayish to brownish tint to it I got some of that cool obsidian from hand2mouthmining also  |
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Post by FrogAndBearCreations on Jun 23, 2012 19:12:17 GMT -5
Frank, why do you think it is glass? I don't care which it is, but I do want to know how to tell the difference. you will NEVER find obsidian in clear colors like that purple or some of the clear grass to dark green, or bright clear yellows they pass off as obsidian the man made glass colors just don't exist in the obsidians, if you ever go and find any out rock hunting let us know because it will be very rare! |
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Post by Pat on Jun 23, 2012 19:24:33 GMT -5
Frog, that would indeed be fun! Last time we went to Davis Creek, we were informed it was the first day of hunting season!! Kept on going!
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RocknCritter
spending too much on rocks
Member since November 2008
Posts: 489
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Post by RocknCritter on Jun 23, 2012 20:02:31 GMT -5
Just caught a small typo in Helen's description above. It's the bit about meteorites being natural glass. This should be moldavite. Otherwise a great description of obsidian.
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how do I tell the difference when it comes to glass that looks a lot like obsidian? Does obsidian fall within an sg range that glass generally does not? Is obsidian conductive in the least relative to glass (it does have a lot of iron it it - I have one piece of sheen that is magnetic) - ?
