February, 2000

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"Fluffy" Type "A" Calcium Aluminum Inclusions

Analysis and description by:
Russell Kempton, New England Meteoritical Services

Refractory inclusions or CAI's (Calcium Aluminum-rich Inclusions) are a mineralogically and chemically diverse group of structures mainly seen in carbonaceous chondrites.

CAI's have complex evolutionary histories. Most involving several episodes of processing within the solar nebula and later, after accretion, within parent bodies.

Through intense study, CAI's have provided significant insights into the physical and chemical conditions present in the solar nebula and have helped to constrain some of the very high temperature processes such as evaporation, melting, and condensation present during the very early stages of our solar system.

Our understanding and classification of CAI's is primarily based upon studies of CV chondrites, mainly Allende. Although essentially all of the different types of CAI's that are known can be found in other chondrites, all are found in CV's.

The image above is "Allende" and a "Fluffy" Type "A" CAI.

Fluffy Type A's are perhaps the most altered of CAI's. The intense alteration and subsequent recrystallization of FTA's obscure original grain shapes, grain-to-grain contacts and textures. The primary mineral assemblage of these inclusions is melilite, V-rich spinel, perovskite, and hibonite.

Photograph Copyright © 2000, New England Meteoritical Services. Index

Reference Sources: "Planetary Materials", Reviews in Mineralogy, Volume 36, 1998

MacPherson, G.L. and Grossman, L. 1984, "Al-rich inclusions in the Allende meteorite"

Meteorites and the Early Solar System, Kerridge, Matthews, "Primitive Material: Refractory Inclusions", G.L. MacPherson et al., 1988