How can I tell if my rock is a meteorite?
Look for a thin dark fusion crust, unusual weight for the size, attraction to a magnet and, on a broken face, metal flecks or small round grains. No home test is conclusive, so an expert must confirm it.
Most meteorites share a few clues, and a genuine one usually shows several of them together. The first is the outside. A freshly fallen meteorite has a fusion crust, a thin black skin less than about a millimetre thick, formed when its surface melted as it raced through the air. Older meteorites may have rusted to brown. Many have rounded edges and shallow thumbprint-like dents called regmaglypts, but no gas bubbles.
The second clue is weight. Most meteorites contain iron-nickel metal and feel noticeably heavier than an ordinary rock of the same size. Iron meteorites feel astonishingly heavy. The third is magnetism: most meteorites will attract a magnet, often quite strongly. Hang a magnet on a thread and see if it swings towards the stone, which also picks up weak attraction.
The fourth clue is inside. If the stone already has a broken or chipped surface, look at it with a magnifying glass. Many stony meteorites show tiny shiny flecks of metal and small round grains called chondrules, set in a grey background. Don't break or cut a stone to check, as experts can grind a small window if needed.
Things that point away from a meteorite include bubbles or holes, layering, quartz crystals, a red-brown or black streak on an unglazed tile, and a glassy, bubbly look typical of industrial slag. Rocks that pass every home test can still be iron ore or slag, so treat these clues as a sieve, not a verdict. A museum or university geology department can confirm a meteorite properly, usually by examining a thin slice under a microscope and measuring its chemistry. Never use acid, heat or tasting to test a rock.