Identifying things that people bring into the museum is one of the many things we do in the Collections Study Centre. We always have a steady stream of people bringing in rocks which they hope are meteorites but so far they have always turned out to be iron stone nodules or slag. David Gelsthorpe, Curator of Earth Sciences at the Manchester Museum has put together a handy list to help you identify whether your rock really is a meteorite.
If your rock is a meteorite it will have:
A fusion crust – A black ash like crust on the surface which looks a bit like an egg shell. This weathers to a rusty brown colour after several years.
Ragmaglypts – The surface of a meteorite is generally very smooth and featureless, but often has shallow depressions and deep cavities resembling clearly visible thumbprints in wet clay.
Be extremely dense – Iron meteorites are 3.5 times as heavy as ordinary Earth rocks of the same size, while stony meteorites are about 1.5 times as heavy.
Be magnetic – Almost all meteorites attract a magnet, because they contain lots of iron.
However if your rock has the features below it definitely is not a meteorite.
Bubbles or holes – If you see holes or frozen bubbles on your rock, these are most likely from gas bubbles that have frozen on the surface of slag. Slag is the waste product skimmed off industrial processes such as iron smelting. Some volcanic rocks contain holes and bubbles from frozen gas in lava.
Crystals – Meteorites never show white quartz crystals. These form in the conditions created by plate tectonics on Earth. Other brightly-coloured crystals or grains in the rock mean the rock is probably slag.
Heat – Most meteorites are cold when they hit the Earth’s surface and do not start fires on the ground. Their trip through the atmosphere is short and the friction heat that burns up the outside does not have a chance to heat up the inside of the meteorite. Meteorites are made of the same elements and minerals as terrestrial rocks and are not any more radioactive than terrestrial rocks.
Streak – If you drag a meteorite across the back of a tile it will not leave a coloured mark. If it leaves a black-grey streak it is most likely magnetite, a red-brown streak means hematite.
Chemistry – Meteorites contain the element Nickel, manmade iron does not.
If you are still unsure if you have found a meteorite come to one of our identification sessions.
Rock Drop is a monthly drop in identification service where David Gelsthorpe is on hand to answer any queries and take an expert look at any rock or minerals (not just meteorites). It is the 4th Thursday of the month in the Collections Study Centre. Form more information visit our webpage http://bit.ly/MMstudy
Alternatively we run a drop off service where items can be left for David to look at, this can take several weeks.