Why does my rock stick to a magnet if it isn't a meteorite?
Many Earth rocks and man-made materials are magnetic, including magnetite, some haematite, slag and iron objects. A magnet test is only a first clue.
Most meteorites contain iron-nickel metal and attract a magnet, so the magnet test is popular. But many things on Earth are magnetic too, and they far outnumber meteorites.
Magnetite. This black iron oxide is strongly magnetic. It occurs in many igneous rocks, in black beach sands and as concentrated ore. A lump of magnetite is heavy, dark and magnetic, just like an iron meteorite, but gives a black streak on an unglazed tile and contains no nickel.
Haematite. Haematite is usually only weakly magnetic, but some samples contain magnetite and attract a magnet. It gives a red-brown streak. Its dark, heavy nodules are often mistaken for meteorites.
Slag. Waste from iron smelting and other industries often contains magnetic iron and iron oxides. Slag is very common and often looks glassy, bubbly or swirled.
Iron objects. Pieces of cast iron, steel, old machinery and cannonballs are magnetic. Man-made iron usually lacks the nickel found in meteoritic iron, and may show signs of casting or manufacture.
Basalt and other volcanic rocks. Some contain enough magnetite to attract a magnet weakly.
What to do. Use the magnet as one test among several. Look for fusion crust, metal flecks inside, chondrules and a lack of bubbles and layers. A streak test helps rule out iron ores. In the end, laboratory analysis, such as testing for nickel and examining a polished section, is needed to confirm a meteorite.