A discussion about a rock (picture to your right): Quimby: Hi everyone, my gran found this rock in Lincolnshire, UK about 30 years ago, and she always believed it was some sort of meteor or asteroid. I've had a look about online, and the closest thing I can find is scoria, but I still can't be sure. The rock is very light, and completely covered in bubbles - there is no flat or smooth surface on it anywhere. Anyone know for sure what it is? Thanks in advance
Geology1: That is absolutely scoria, a textbook example.
Petronut: I hate to have to disagree, but this is definitely not scoria. In fact, I don't believe it is even basalt. I'm not sure what is the cause of the pattern, but those are not vesicles created by trapped gas. It almost looks like a pseudo-morph, but of what, I do not know. I'm not even sure what the rock is or even if it's igneous or sedimentary. It is an interesting mystery. It almost looks like the inside of a wasp's nest. But, I don't have a clue as to what it is. I just know it's not scoria.
Quimby: Thanks for taking a look Petronut, at least I now know its either definately scoria or definately not scoria. lol! Anyone else have any thoughts on this? Where might I be able to find out for definate and more importantly how much will it cost?Thanks again!
Petronut: Most university geo-science departments around the country are happy to help you indentify a specimen free of charge.
Geology1: Well, we have two opposing interpretations, for which neither of us has adduced any evidence. So let me start by saying what leads me to my fairly confident ID. First of all, it could also be slag, say from steelmaking. Both volcanoes and industrial processes yield lightweight, bubbly, dark, stony products. Here is a volcanic scoria:http://geology.about.com/od/rocks/ig/igrockindex/rocpicscoria.htm Here is a piece of slag: http://geology.about.com/od/rocks/ig/artificialrocks/slag.htm Slag is generally softer and crumblier than scoria. Scoria will scratch glass; slag may not. For scoria it is unusual in the large size and even consistency of its bubbles (for slag it is even more unusual), but here's a specimen that's similar at a much smaller scale: http://geology.about.com/od/more_igrocks/ig/extrusives/scoriaAK.htm Your specimen has been rounded, evidently in a river or on the beach. It could have floated to Lincolnshire from Iceland. Does it float?
Petronut: I just realized what this is! I don't know why it didn't occur to me sooner. This is a specimen of colonial coral in shale! What genus it is, that I can't say. But I think the genus might belong to the Order Scleractinia. Probably from the Miocene to the Pleistocene.
Geology1: Could you point us to some similar examples? I'm afraid I don't see the resemblance.
Petronut: Here's a link to an image of Septastraea marylandica, another genus in the Order:http://www.mondowendell.com/septastr.html Can you see the resemblance now?
Geology1: No, I see a finely detailed limy structure with interior features, a very clear example of a fossil. The image in this thread, instead, is a clean set of smooth bubbles in an aphanitic dark material with every appearance of a basalt. I think the images speak for themselves.
Petronut: Geology1, this is just one of literally hundreds if not thousands of genera for this Order. This isn't even the same genus! I don't know what the genus is and unless you have a university library at your disposal and are willing to look through literally thousands of photos and/or illustrations, you're not going to find out what genus this is. In fact I don't even know what the phylum is. I never said this was a fossil of the same organism, only that it was probably in the same Order. You do know the difference between species, genus, phylum and Order, don't you?
Geology1: Petronut, this rock really is not a coral. Seriously, it's gas bubbles in a rock that was once fluid. I don't want to presume, but I wonder if your geology courses involved visiting volcanic regions. If you visit Hawaii, or any of the western states, you can find rock that looks exactly like this associated with volcanoes. My only hesitation in calling this rock a scoria is that I'm not familiar with English geology in any detail. There are fairly recent volcanic rocks in the west, but volcanic rocks of this freshness are more likely to come, as I suggested, from the waters around Iceland. You still have not said what leads you to think this cannot be scoria.
Petronut: If you go to this link in my Web site, you will see that I have three volcanic bombs from Australia in my collection:http://home.comcast.net/~ericfjdiaz/images_extrusive_igneous_rocks.html I've seen basalt in just about every form that it comes in, fresh out of the ground, heavily weathered, degassed, ropey, pillow lavas and yes....tons and tons of scoria! Igneous petrology is one of my areas of concentration, and I'm telling you with absolute certainty that that is not scoria. Let us agree to disagree. ;-)