What type of rock is this?

[lee]

We had a lake dug out several months ago and the small rock below was chipped out of a red boulder that was unearthed during the process. It looks like a fossil to me, it has the look and texture of coral. It could be some sort of lava because the top is shiny like glass and the bottom has flecks of gold coloured rock. It's quite heavy and is tough enough to scratch glass and metal.

Any geologists out there that can identify it?

[rick]

Cannot do from a photo. Also the red boulder it was in would help - does it include any other embedded rocks and what is the boulder made of? I used to work as a geologist, long time ago.

[maaka]

wild guess, rough obsidian with which has picked up some other minerals during the volcanic stage..
I have boulders of obsidian at home, mainly smooth as black glass, but some are rough..the red throws me abit but that could be a clay mixed in, some of that Thai clay is pretty red..take to the little jewellry shop afew doors up from the library..they cut and make thier own stuff onsite..they may know for sure..indeed, if it was cut and polished it might make a nice pendant / brooch for the missus..

[lee]

Also the red boulder it was in would help - does it include any other embedded rocks and what is the boulder made of? I used to work as a geologist, long time ago.

I'm not sure what type of rock it was in however it's a common rock that you see everywhere, it looks like lava and is very heavy, the garden centers cut this rock up to make paving slabs. The photo below shows the type of rock it came from, there weren't any other embedded rocks in it.

if it was cut and polished it might make a nice pendant / brooch for the missus..

Funny you should say that, the guys digging the lake suggested making a Buddhist pendant out of it.

[parrot]

If I was looking for a lucky number for this month's lottery, I'd be staring at the face in the lower right hand corner of the photo. Its right eye is open along with its mouth. I'm sure a Thai would be able to determine what lucky number the Pii is trying to say.

[rick]

Right. Some Volcanic rocks can contain fragments of older rocks which break off as the lava forces its way through older rocks; sometimes these melt into the lava but sometimes they survive. Typically if from deep within the earth these are more basic (contain less silicon dioxide, and more metallic minerals); these rocks are usually, heavy, dark and can contain iron minerals like magnetite (can test for this if you have a compass - it will be deflected if held close) The white bits are probably amorphic quartz (i.e. silicon dioxide). The gold colour is probably Mica - if you rub it some should rub off and be like small flakes). Obviously this is just my guesswork based on the photos and possibly volcanic origin.

[lee]

Thanks Rick. I'll see if I can get my hand on a compass to test for magnetite. Yes the gold does rub off so your analysis is probably correct. Oh well that crosses a potential gold mine off my list. LOL

BTW do you know what that common red rock is called?

[rick]

Lee, cannot really tell very much about the red rock from the picture. But I am thinking maybe not Volcanic - most rocks in this part of the world are Sandstones, gravels, conglomerates (stones cemented together) and a few limestones. But what i was wondering, assuming the 'rock' is not that strong (can you scrape bits off easily?) is that maybe it is laterite - soils which have been highly weathered, usually low in silica and mainly a mixture of iron and aluminium oxides. Laterites are common in the tropics and are responsible for the red roads everywhere. Laterites are not always soft (unless crushed) and apparently is cut into blocks in India and used instead of bricks. As they are derived from soils,already broken from other rocks and maybe transported around by the elements, often have stones of more resistant material in them.

Hope you like the geology lessons!