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It is beyond the scope of this book to examine these non-carbonate grains in detail, but a few of the more important types—clastic terrigenous grains, glauconite “pellets”, and ferruginous and phosphatic ooids—will be discussed briefly. The criteria for their recognition and the compositional characteristics of these grains are given in the individual figure captions.

The recognition of non-carbonate grains in carbonate rocks is important for the interpretation of depositional environments and for the proper classification of mixed-composition rocks. Most specialized classifications of carbonate rocks simply use adjectives such as “quartzose”,“very quartzose”,“feldspathic” or “glauconitic” to note the presence and relative abundance of non-carbonate grains (the term “silicified” is appropriately used where a significant amount of silica replacement has affected the deposit).