chondrite

A chondrite is a stony (non-metallic) meteorite that does not show signs of overall melting. They typically include round grains (chondrules) which are interpreted as rapidly melted and cooled aggregates of cosmic dust and assumed to be material formed very early in the life of the solar system. The melting that a chondrite did not experience is any subsequent melting that would smooth away the grains. There is not a consensus on the details the formation of these chondrules, i.e., what caused the required heating and cooling. Theories:

• Nebular shock - heat from shock waves forming in solar nebula.
• Impacts involving planets.
• Space lightening - sparks in plasma.
• Early coronal mass ejections, e.g., from strong magnetic fields in the Sun's pre-main-sequence stage.
• Impacts involving solar system bodies smaller than planets, i.e., asteroids, planetesimals, etc.
• Some of each of the above.

The term achondrite refers to such meteorites that do not include chondrules, generally presumed to have formed at a later time.