Glass with embedded metal and sulfides (GEMS) are tiny spheroids in cosmic dust

Cosmic dust

Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 µm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust .In our own Solar...

 particles with bulk compositions that are approximately chondritic. They form the building blocks of anhydrous interplanetary dust particles

Cosmic dust

Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 µm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust .In our own Solar...

 (IDPs) in general, and cometary IDP

Cosmic dust

Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 µm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust .In our own Solar...

s, in particular. Their compositions, mineralogy

Mineralogy

Mineralogy is the study of chemistry, crystal structure, and physical properties of minerals. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, as well as their utilization.-History:Early writing...

 and petrography

Petrography

Petrography is a branch of petrology that focuses on detailed descriptions of rocks. Someone who studies petrography is called a petrographer. The mineral content and the textural relationships within the rock are described in detail. Petrographic descriptions start with the field notes at the...

 appear to have been shaped by exposure to ionizing radiation. Since the exposure occurred prior to the accretion

Accretion (astrophysics)

In astrophysics, the term accretion is used for at least two distinct processes.The first and most common is the growth of a massive object by gravitationally attracting more matter, typically gaseous matter in an accretion disc. Accretion discs are common around smaller stars or stellar remnants...

 of cometary IDPs, and therefore comets themselves, GEMS are likely either solar nebula

Solar nebula

In cosmogony, the nebular hypothesis is the most widely accepted model explaining the formation and evolution of the Solar System. There is evidence that it was first proposed in 1734 by Emanuel Swedenborg. Originally applied only to our own Solar System, this method of planetary system formation...

 or presolar interstellar grains

Presolar grains

Presolar grains are isotopically-distinct clusters of material found in the fine-grained matrix of primitive meteorites, such as chondrites, whose differences from the surrounding meteorite suggest that they are older than the solar system...

. The properties of GEMS (size, shape, mineralogy) bear a strong resemblance to those of interstellar silicate

Silicate

A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...

grains as inferred from astronomical observations. Bradley and Ireland, 1996