Calcium Aluminum-rich Inclusion

Calcium Aluminum-rich Inclusion from NWA 6231 (CK4). Image Credit: Mendy Ouzillou

Sub-millimeter to centimeter-sized amorphous objects found typically in carbonaceous chondrites and ranging in color from white to greyish white and even light pink. CAIs have occasionally been found in ordinary chondrites, such as the L3.00 chondrite, NWA 8276 (Sara Russell, 2016). CAIs are also known as refractory inclusions since they are comprised of high-temperature refractory minerals, including silicates and oxides of Ca, Al, and Ti. In 2002, an international team of scientists accurately dated CAIs at 4.567 Ga, making them the oldest (earliest formed) known objects in the solar system. The same team found that chondrules, another of the earliest relics of the solar system, formed 2-3 Ma after CAIs. Both types of object formed when dusty regions of the solar nebula experienced transient heating events of, at present, an unknown origin. The dust melted and then crystallized, forming first CAIs and during later event(s), chondrules.

“CAIs formed by evaporation, condensation, and aggregation in a gas of approximately solar composition in a hot (ambient temperature >1300 K) disk region exposed to irradiation by solar energetic particles, probably near the protoSun. Subsequently, some CAIs were melted in and outside their formation region during transient heating events of still unknown nature.”1

There are three types of CAIs:

  • Type A CAIs are melilite-rich, fine-grained and irregularly shaped. There are also type A CAIs called fluffy CAI.
  • Type B CAIs are coarse-grained, consisting of Al-Ti-pyroxene (fassite), melilite, anorthite and spinel.
  • Type C CAIs are anorthite-rich and coarse-grained.

Some or all content above used with permission from J. H. Wittke.