How can I tell a meteorite from slag?
Slag is usually bubbly, glassy or swirled, often lighter than expected and may have flow textures; meteorites are dense, have a thin crust and no bubbles inside.
Slag is the waste material left over from smelting metals and other industrial processes. It is extremely common and is probably the most frequent meteorwrong brought to museums.
What slag looks like. - Bubbles. Slag usually contains many round gas bubbles, inside and on the surface. - Glassy texture. It often has shiny, glassy surfaces, sometimes with swirls or flow patterns. - Colours. It can be black, grey, brown, green, blue or iridescent. - Weight. Some slag is heavy and magnetic, containing iron, but much is lighter than expected for its size. - Shape. It may have drips, ropes or flat surfaces where it cooled against moulds or the ground. - Location. It is often found near old industrial sites, railways, roads, farm tracks and beaches.
What meteorites look like. - No bubbles inside in almost all types. - Thin fusion crust, about a millimetre thick, matte or slightly shiny, not thick glass. - Interior grey with metal flecks or chondrules, or solid metal in irons. - Dense and usually magnetic.
Simple tests. - Break or look at a broken surface of slag: you will usually see bubbles or glass. Do not break a suspected meteorite. - Streak test: some slag leaves a dark streak; most meteorites leave little.
Why it matters. Slag is so common that it is a good reason to be cautious before getting excited about a find. If in doubt, photographs to a museum or identification service will help.