One of the three largest grouping of meteorites is the stony-iron group of meteorites. These meteorites are as the name indicates made of both nickel iron metal and stone. Though other iron meteorites may have mineral components within their makeup. In the case of the stony-irons the amount of stone is much greater. This group includes two large sub groups the pallasites and the mesosiderites.
The Pallasite class of meteorites is characterized by meteorites that have a large portion of their mass in the form of olivine crystals. Generally, these crystals are yellow, golden or in some cases green like the peridot that olivine is known for from earthly sources. The crystals are surrounded by nickel-iron. This is by its very nature something of a puzzle. Since it is like oil and water mixing to have these crystals mixed with metal. Scientists continue to work on models which will explain the formation of pallasites. But, these mysterious meteorites are the most beautiful of all when cut and polished or also etched in some cases.
Mesosiderites Silicate minerals are found quite commonly in many varieties of iron meteorites. However, when the amount of silicates gets quite high these meteorites are often classified as mesosiderites. The minerals are pyroxenes and feldspars generally in mesosiderites. This is in contrast to olivine which is found in pallasites. The similarity of composition between mesosiderites to some of the achondrites is prompting some scientists to reevaluate whether they are really to be classed with the stony-irons. They may someday be associated with some of the achondrites. Mesosiderites are some of the most interesting of the meteorites visually and being quite uncommon makes them some of the most desirable to collect.