Some meteorites, called CI chondrites, contain quite a lot of water; more than 15% of their total weight. Scientists have suggested that impacts by meteorites like these could have delivered water to the early Earth. The water in CI chondrites is locked up in minerals produced by aqueous alteration processes on the meteorite’s parent asteroid, billions of years ago. It has been very hard to study these minerals due to their small size, but new work carried out by the Meteorite Group at the Natural History Museum has been able to quantify the abundance of these minerals.
A CI chondrite being analysed by XRD. For analysis a small chip of a meteorite is powdered before being packed into a sample holder. In the image, the meteorite sample is the slightly grey region within the black sample holder. The X-rays come in from the tube at the right hand side.
The minerals produced by aqueous alteration (including phyllosilicates, carbonates, sulphides and oxides) are typically less than one micron in size (the width of a human hair is around 100 microns!). They are very important, despite their small size, because they are major carriers of water in meteorites. We need to know how much of a meteorite is made of these minerals in order to fully understand fundamental things such as the physical and chemical conditions of aqueous alteration, and what the original starting mineralogy of asteroids was like.