Chondrules; The Main Material in the Formation of Planets

and among the oldest material in our Solar System.


Chondrules in Ordinary Chondrite

WHAT ARE CHONDRULES


Chondrules are spherical structures found in a special class of stony meteorites called chondrites. Chondrites represent 86% of all the meteorites that fall on Earth.


WHY ARE THEY SO SPECIAL


Chondrules were among the first constituents of the Solar System, formed 4.56 billion years ago. They are the building blocks of planets. In chondrites, we can find chondrules unchanged since their formation, so they offer us a privileged glimpse into the beginnings of our Solar System.


THE FORMATION OF CHONDRULES


They were formed as a result of the rapid heating event, which produced melt, followed by rapid cooling. Sudden temperature difference has trapped the material inside chondrules. The origin of the heating event is yet unknown.The most likely causes of the event are nearby supernova explosion, shock waves in a protoplanetary disk and solar activity. The formation of the melt is also the reason for their spherical shape.


TYPES OF CHONDRULES AND MINERAL COMPOSITION


Chondrules are divided into two main types: porphyritic and nonporphyritic. Porphyritic chondrules (LEFT) were formed as a result of the aggregation of mineral grains around common nucleation point. Nonporphyritic chondrules (RIGHT) were formed during the rapid heating event directly from the melt.

By their mineral composition they are subdivided into olivine (PO), porphyritic pyroxene (PP), porphyritic olivine pyroxene (POP) and granular olivine pyroxene (GOP). Nonporpyritic chondrules are divided into barred (BO) olivine, radial pyroxene (RP) and cryptocrystalline (C).



THE SIZE OF CHONDRULES


The size of chondrules is related to the subgroup of chondrites: on average it is 0.5 – 1 mm. However, in some meteorites chondrules larger than 1 cm can be found. In general, it is very difficult to see chondrules in an unpolished rock. They are usually observed using crossed-polarized light in an optical microscope or with scanning electron microscope (SEM).




Chondrules are one of the most amazing materials found in meteorites and on Earth. And you can have them at home! Meteorites have great scientific value and even more amazing stories surviving the outer space environment.



Writing for Stellar Delight: Bojan Ambrozic, Master of Science in Meteoritics

Images courtesy: Bojan Ambrozic

©2020 by Stellar Milieux