How Do I Identify a Space Rock?

Posted: October 3, 2011 - 12:06 , by Ian Nicklin
Natural History, Meteorites, Mineralogy, Research | Comments (9) | Comment

Originally published in ROM Magazine, Fall 2010.

I found a blackened rock that I think might be a meteorite. How can I tell for sure?

It is widely held that a picture is worth a thousand words. In the case of meteorites or more often meteor-wrongs—the all-too-terrestrial objects that are mistaken for meteorites—this is particularly true. Every year the ROM’s Earth Sciences section receives dozens of e-mails, letters, and phone calls from people who have found an unusual rock that they suspect is a meteorite. It’s easy to understand why. Written descriptions of meteorites usually specify a blackened, charred, or “burnt” exterior with surface pitting, sometimes referred to as thumbprinting. Less often “heavy” and magnetic” are also included as criteria.

The problem is that these “diagnostic” features are commonly mimicked by industrial by-products, such as slag.  Slag does have a quite striking, other-worldly appearance and is often found in unlikely places—which naturally leads people to suspect that it has fallen from the sky.  But given Toronto’s industrial past, and the number of landfills in which slag was a common component, it’s not all that surprising that slag turns up in seemingly impossible places.  To this day it is still reguularly found in railroad beds.

Like true meteorites, slag does have a melted or burnt appearance because it was at one time molten.  But unlike meteorites, which are charred from enduring the passage through out atmoshpere, slag is charred in a blast furnace, and it surface can be even more tortured than that of most meteorites.  Like meteorites, slag is often heavy and sometimes quite magnetic, since smelting is typically not 100 percent efficient, and iron may remain within it.

So how do we tell the difference?  The telltale characteristic is bubbles.  Gas bubbles are rare in true meteorites but nearly ubiquitous in slag.  Another difference is that slag is a glassy material that shatters with the characteristic scalloped or “conchoidal” fracture of glass while real stony meteorites break more like terrestrial rocks.

The ROM owes a debt to readers like yourself who are out paying attention to your surroundings and noticing odd, out-of-place objects.  This is how discoveries are made.  But it often takes a practiced eye to pick out the differences between true meteorites and Earth rocks that mimic their appearance.  Fortunately, the ROM offers a large display of “Meteor rights” in the Teck Suite of Galleries: Earth’s Treasures, where visitors can see many examples of the real thing.

Join us for the next Rock, Gem, Mineral, Fossil and Meteorite Identification Clinic on November 16, 2011.  Bring your space rocks and other treasures for a ROM expert to id.

Slag vs Meterorite: how to differentiate

A slag specimen pictured on right. A meteorite pictured on left.

Left: This sample of slag has large bubbles, or vesicles as they are sometimes called, which are very rare in real meteorites. Slag also fractures like glass. Right: Stony meteroites such as this one break not like glass, but like normal terrestrial rocks.



Comment by Mary

we located a very heavy silver rock in a hole were where digging in Toronto.
when a shovel hits it is sounds like steel.
What can we do with it. Is it valuable?
please let me know.

Comment by Beverley

I've had a silver black rock for years and when you put different light on it, it glows orange and blue and has an emerald green to the inside which was broken off a bigger rock. The surface is really smooth with long streaking lines but the inside is rocky green and a creamy color with a green glow. The glow from lights make it look like there are some kind of crystals glowing underneath the silver coating. On angles you can really see the orange and it looks like the whole thing underneath is completely crystal. On a certain angle when I videoed the rock it had such white glowing streaks showering from it. And after videoing it my camera icons were spinning around for a while. It's very strange. Who can I show this to?

Comment by Lead Concierge

Hi Beverley, visitors with rocks, minerals, gems, fossils or suspected meteorites can have them identified at these special ID clinics held six times a year.  These clinics are free, however NO appraisals will be done.  The dates for 2015 are:  February 18, April 22, June 17, August 19, October 14 and December 9.  All are held on a Wednesday from 4:00-5:30pm.

Comment by Angelo Sciarra

I my name is Angelo Sciarra like lot other people I found a rock in my yard a rock that was not there wen I cut the grass.The rock is 1800 gr.shape like other space rocks pictures from the computer,so will be nice if an expert will look at them.I will like to be present to your Dec.9 2015 at the Royal Ontario Museum.
Thank you.
Angelo Sciarra

Comment by Kevin

I found this rock on the side way in front of my parents place last year in the summer. It's black with shiny particles on it. It has small craters and also rough edges. It's black with some brown colouring to it. And very magnetic. I would like to visit the ROM some day and see if it's the real deal. When is the clinic open? Thank you.