How do I test a rock for nickel?
Specialists use chemical spot tests that turn pink in the presence of nickel, or instruments such as X-ray fluorescence. A home test needs a cleanly ground metal surface and chemicals, so it is best left to experts.
Nickel matters because nearly all meteoritic metal contains it. The iron-nickel metal in meteorites typically holds at least about 5 per cent nickel, and often more, whereas most rocks on Earth's surface contain very little native metal of any kind. Finding nickel-bearing metal in a stone is therefore a strong hint that it came from space.
The classic chemical method uses a reagent called dimethylglyoxime, often shortened to DMG. When a drop of the test solution touches nickel on a freshly exposed metal surface, it turns a striking pink to red colour. Commercial kits exist for testing jewellery and metals. In a laboratory, scientists more often use an X-ray fluorescence analyser, which measures the elements in a surface without chemicals, or an electron microprobe, which analyses individual mineral grains within a polished slice.
There are good reasons to leave this to experts. The test only works on bare metal, which usually means grinding or cutting into the stone, and that can damage a valuable specimen. The chemicals involved can be harmful, so they are not suitable for children. Results can mislead, too. Stainless steel and some other manufactured alloys contain nickel, so a scrap of industrial metal can test positive, while a stony meteorite may test negative simply because its metal grains are tiny or not exposed.
A better plan for most people is to send clear photographs, the weight and the result of a magnet test to a museum or university geology department. If the specimen looks promising, they can arrange a proper analysis without harming it. As always, avoid acid, heat and cutting at home, particularly with children around.