Main mass
The main mass is the largest single piece recovered from a meteorite.
When a meteorite is found in several pieces, or later cut up for study, the biggest surviving piece is called the main mass. Specimens cut or broken from it are smaller pieces of the same meteorite and share its name.
Main masses matter for several reasons. They are often the best-preserved part of a meteorite and give a sense of its true size. Museums treasure them, and when a new meteorite is officially named, a reference sample called the type specimen must be lodged with a recognised collection. For the Chelyabinsk fall in Russia in 2013, the main mass is a stone of about 540 kilograms that divers lifted from the bed of Lake Chebarkul in October that year; it is now on public display in Chelyabinsk.
The term is used flexibly. For a meteorite that fell as one stone, the main mass may simply be the largest remaining block after slices have been removed. Collectors sometimes see the words "main mass" in a catalogue, which signals the most important piece rather than an offcut.
Related terms
Level: Explorer Ages 10 and up