Classification of Rocks Essay

For instance, if a rock is composed of odds, it is termed and Elliott limestone. If the limestone also contains a minor element such as skeletal fragments, then it is called a collectivities limestone. Two of the most widely used classifications are those of Folk (1 959,1 962) and Dunham (1962). Both classifications subdivide limestone primarily on the basis Of matrix content. Most limestone are classified by Folk alchemical rocks if they contain over 10% allocates (transported carbonate grains).

Based on the percentage of interstitial material, the rocks may be further subdivided into two groups: Sperry alchemical limestone (containing a Sperry calcite cement of clear coarsely crystalline mosaic calcite crystals) and incrementally alchemical limestone(containing incrementally calcite mud, mimicries, which is subcontracted grayish or brownish particles less than about 5 microns in size). Further subdivision is based on the allocate ratios of Folk (1962) are shown in Schools & Elmer-Schools (2003).

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Thus Folk’s classification (figures above) is most suited for thin section study. Remember that he terms rocks with appreciable matrix as mimicries while matrix-free rocks that contain Sperry calcite cement are termed spa rites. As you can see sprites and mimicries are further subdivided by means of their most common grains. In contrast, Dunham classification (figures above) and its modification by Embryo and Kaolin (1971) and James (1984) deals with depositional texture.

For this reason, his scheme may be better suited for rock descriptions that employ a hand lens or binocular microscope. For example, if the grains of a limestone are touching one another and the sediment contains no mud, then the sediment is called a gravestone. If the carbonate is grain supported but contains a small percentage of mud, then it is known as a backstops. If the sediment is mud supported but contains more than 10 percent grains, then it is known as a wastebasket, and if it contains less than 10 percent grains and is mud supported, it is known as a mudstone.

If one compares the two allocations, a rock rich in carbonate mud is termed a mimicries by F-look and a mudstone or wastebasket by Dunham. Moreover, a rock containing little matrix is termed a spirits by Folk and a gravestone or backstops by Dunham. The wide range of percentage of mud matrix that a carbonate may have and still be termed a backstops by Dunham sometimes reduces the utility of this classification. Embryo has modified Dunham classification and Kaolin (1971) to include coarse grained carbonates (above figure).

In their revised scheme, wastebasket in which the grains are greater than mm in size is termed a flagstone and a coarse gravestone is called a Redstone. Both terms are extremely useful in description of limestone. Embryo and Kaolin to more graphically reflect the role that the organisms performed during deposition also modified the bounteous classification of Dunham. Terms such as bafflement, bondsmen, and freestone are useful in concept but are extremely difficult to apply to ancient limestone where disengages and sample size limit ones ability to assess an organisms function.