GUIDE TO THE DIFFERENT TYPES OF METEORITES: IDENTIFICATION AND ORIGINS

Primitive meteorites are formed from the original material that formed all objects in the Solar System. Among the most common are chondrites, which represent about 86% of the meteorites found on Earth. Chondrites get their name from the chondrules, small spherical mineral grains, that they contain. These chondrules are intact remnants of the first solids formed in the Solar System, preserving crucial information about the conditions and processes that prevailed when it formed billions of years ago. Chondrites are divided into several groups, including ordinary chondrites and carbonaceous chondrites, each with distinct characteristics and significant implications for astronomy and geology research.

Differentiated meteorites come from a celestial body large enough to see its original material melt and then separate into different layers. The latter are divided into three main categories: achondrites, ferrous and lithosiderites.

Achondrites come from celestial bodies that have undergone partial or complete differentiation. Unlike chondrites, achondrites do not contain chondrules and often show crystalline textures or mineralogical compositions similar to those of terrestrial rocks. Their study allows us to better understand the processes of formation and differentiation of celestial bodies, thus providing insight into the internal mechanisms of planets and asteroids. Regolith Breccia and Shergottite, present in the MOON and MARS bracelets, are part of this category of meteorites representing just under 7% of celestial objects in world collections.

The last category is made up of iron meteorites , composed mainly of nickel and iron. These meteorites are distinguished by their shiny metallic appearance and impressive weight. They generally come from the cores of differentiated celestial bodies such as asteroids or planets. The study of iron meteorites allows us to better understand the composition and evolution of planetary cores, as well as the metallization processes that shaped the early stages of the formation of terrestrial planets. Among these iron meteorites, some have undergone a particular process that gives them striated patterns called Widmanstätten Figures, which are found in Muonionalusta (meteorite present in IRON bracelets ).

Lithosiderites , also known as mixed meteorites, are characterized by a varied composition including both ferrous parts, such as iron and nickel, and silicates. This category is divided into two distinct categories: mesosiderites, for example, those present in the ATLAS bracelet , and pallasites, whose origin is debated.

Lithosiderites already represent only about 1% of observed meteorite falls, mesosiderites are even rarer. These are breccias composed of silicates and iron-nickel in relatively equal proportions, accompanied by troilite. They are characterized by a silicate material formed of fine matrix grains and larger grained clasts. These meteorites are classified into three categories according to the percentage of orthopyroxene they contain. Unlike pallasites, mesosiderites are the result of a mixture of materials from both the crust and the core, which suggests a probable formation by impact.

Pallasites , on the other hand, consist of silicates, mainly coarse-grained olivine, iron-nickel and troilite in relatively equal proportions. These meteorites are subdivided into three subgroups according to their mineralogy, chemical and isotopic composition. The characteristic association of olivine and metal in these rocks suggests that they may have originated from the core-mantle interface of a differentiated celestial body (since olivine is a typical mantle mineral) or that they were formed during collisions between planetary debris from the core and the mantle.