Like a Dirty Snowball from the far-flung reaches of our Solar System

Some scientists believe certain meteorites to originate from comets, which have colloquially been termed "dirty snowballs" -- a mixture of frozen water and accreted stony material. Carbonaceous chondrites such as the CI chondrites have never been heated above 50°C during their formation and subsequent history. Otherwise, the water would have rapidly evaporated and the hydrous phyllosilicates would have been metamorphosed into other minerals due to the loss of water.

CI chondrites and the closely related CM chondrites are particularly rich in volatile substances, including water. It is possible that the CI meteorites could have originally formed in the outer solar system, at a distance greater than 4 AU (1 AU is the distance between our Earth and the sun). They were formed beyond our solar system's "snow line", a division representing a temperature of 160° K. At this temperature, any water present in the cometary/asteroidal body would have condensed to ice and been preserved. This is supported by the similarity of CI chondrites with the icy moons of the outer solar system, such as Europa and Triton. Based on mineralogical and chemical evidence, including the high deuterium/hydrogen ratio of CI meteorites, it is possible that the CI meteorites could be fragments of comets or extinct cometary nuclei. These are the extinct bodies of comets that have exhausted their volatiles, losing their tails, and subsequently being captured by the inner asteroid belt between the gravities of Mars and Jupiter.

Here is an article discussing the outer asteroid belt origins of the Tagish Lake meteorite:

"Tagish Lake -- A Meteorite from the Far Reaches of the Asteroid Belt"

"Peter Brown and friends noted that the orbit of Tagish Lake extended to that part of the asteroid belt where asteroids classified by astronomers as C, P and D types predominate. These asteroids are know to have hydrated silicates (water-bearing minerals) on their surfaces, and because of their dark color, are suspected to be rich in carbon compounds. These are also characteristics of the most primitive meteorite types known -- the carbonaceous chondrites, especially the types classified as CI and CM. This was the first clue that Tagish Lake might be a primitive type of chondrite." 

Thought to contain the most primitive matter in our solar system, could Tagish Lake have also been a comet in it's long and mysterious past? D-type asteroids are thought to have originated in the Kuiper Belt, a region of the solar system beyond the orbit of Neptune. Tagish Lake's characteristics strongly suggest that it is a primitive body coming from the far reaches of our solar system.