GeologyRockswhat kind of rock is this?
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what kind of rock is this?
Tue, 09/13/2005 - 04:29Hello foundarock!
At first glance, I'm pretty sure your rock is obsidian. This is a volcanic rock which cools so quickly no crystals can form. It's mainly made of silica (SiO2) and is essentially volcanic glass.
You can test this further by doing a few tests. Silica has a hardness of 7, so try scratching your rock with a penknife - it should be difficult, as a good penknife also has a hardness of 7 (a cheap one, will be nearer 6 and therefore not scratch the rock). Are there any distinct minerals in the rock? You may see some white snowflake-like patterns if it is obsidian, but there are no distinct minerals or grains. The colour looks black from the photo. Is it?
Cheers,
Jon
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what kind of rock is this?
Tue, 09/13/2005 - 13:08Thanks for replying Jon and Gus.
Jon - I tryed the pen knife test but with a scissor edge! does that make a difference? Anyway it is extremely hard to scratch, infact on i couldn't scratch it at all on any of its faces, just over the sharp ridges. It is black in colour and while i can not see any snowflake effect, it does have little fleck/flints of olive green/yellowy in places that reflect in the light. I have looked up pics of obsidian and it does look like it.
Gus - Yeah, lol I posted about this rock on some other forums as well, I wasn't sure how active these forums would be! - I have also looked up pics of slag and the texture and shine doesn't appear to resemble slag from what i can see, but found one pic of 'shiny' slag that it does look like. If it was slag would it leave a black mark if dragged across some concreate? I tryed this and it does not leave a black mark. The little crator holes on one side of it are more like inverted bubbles than holes, like a crator with a bubble in the base.
I know i'm probly being silly, but are such rocks safe to handle, be in the house? lol
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what kind of rock is this?
Thu, 10/13/2005 - 17:53Hi Foundarock
I too have seen your posting elswhere and have done some research. I have come across a rock called Tektite. Tektite is an impact glass from meteorite impact and is a result of great heat and pressure It appears as a black glass and its' surfaces have pitting - or your 'inverted bubbles'!
Do a search and see what you think.
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what kind of rock is this?
Submitted by foundarock on Mon, 09/12/2005 - 21:47.hi all - I was wondering if anyone could tell me anything about this rock i found in my flowerbed. I don't know anything about geology, i found this forum thru a search...The rock is shiny black, smooth on 3 sides like a marble texture. On the other side its full of little crator holes, they look like inverted bubbles almost. The rock weighs 310g.
I put pics on a geocities webpage as im not sure how to load images directly onto here :oops: but the link is
http://www.geocities.com/wispa78/rock.html