506 



UNITED STATES MINERAL RESOURCES 



tacked by fungi and bacteria, and the carbon and 

 hydrogen of the ceUulose unite with atmospheric 

 oxygen and with each other to form carbon dioxide, 

 water, and marsh gas. If oxidation is unhampered, 

 the organic material will disappear in a relatively 

 short time. K, however, the plant falls into water or 

 upon water-saturated soil where atmospheric oxy- 

 gen is largely excluded, decay is slow, and if the 

 plant debris becomes buried, a large proportion of 

 the fixed oxygen is retained, and peat is formed. 

 By this means, peat, which essentially has the com- 

 position C62H72O24, forms from cellulose (C72H120O60) 

 by the elimination of hydrogen and oxygen as water 

 (H2O), carbon and oxygen as carbon dioxide (CO2), 

 and carbon and hydrogen as methane (CH4) (Soper 

 and Osbon, 1922, p. 6-7). 



Peat is formed in swamps, bogs, or marshes under 

 conditions favorable to the profuse growth of plants 

 and to the accumulation of plant debris without 

 complete decomposition by bacterial and chemical 

 action. Climate, topography, and changes in position 

 of the water table are the chief factors governing 

 the formation and preservation of peat deposits. 



The quality of peat is determined by several fac- 

 tors. The rate and type of water inflow and drainage 

 control the amount of inorganic material such as 

 silt, sand, and gravel. Fluctuation of the water table 

 permits air to come in contact with wet peat and 

 causes rapid decomposition, leading to partial or 

 complete destruction of plant fibers. Such fluctua- 

 tion is greatest near streams and drainage ditches. 

 If surface conditions are unchanged, carbonization 

 is largely arrested, and peat forms ; it may continue 

 to exist indefinitely as peat unless the land is drained 

 and decomposition begins, or unless it is deeply 

 buried beneath sediments and subjected to pressure 

 and heat to form coal. 



CLASSIFICATION 



For statistical purposes the U.S. Bureau of Mines 

 has classified peat into three general types — moss 

 peat, reed-sedge peat, and peat humus. Peat of 

 sphagnum, hypnum, and other moss types is classi- 

 fied as moss peat, whereas peat of reed-sedge, shrub, 

 and tree groups is classified as reed-sedge peat. Any 

 peat so decomposed that the botanical identity is 

 lost is classified as peat humus. This classification, 

 however, does not adequately identify peat accord- 

 ing to properties demanded by modern industry, 

 properties which are based on the use of peat as a 

 soil conditioner and horticultural material. 



Chief among these desirable properties is water- 

 holding capacity, or the ability to reabsorb water 

 after initial drying, like a sponge. Water-holding 



capacity, which is measured in percentage by weight, 

 depends upon botanical character, the degree of 

 decomposition, and the extent to which peat has 

 dried. Ash content, also measured in percentage by 

 weight, consists of the solids remaining after a test 

 portion of dry peat has been heated at 550°C. Ash 

 content is therefore the reciprocal of organic content 

 valuable to peat use. Fiber content refers to the 

 proportion of stem, leaf, or other plant fragments 

 between the sizes of 0.15 and 12.7 mm. 



To meet the need for a classification designed 

 principally to characterize different types of peat 

 on the basis of these and other useful properties, 

 such as acidity and moisture content, a new classi- 

 fication was proposed by the American Society for 

 Testing and Materials Committee D-29 Subcommit- 

 tee I (Farnham, 1968) ; this classification was 

 adopted in the form of ASTM Designation D2607- 

 69 (Am. Soc. Testing and Materials, 1969). Accord- 

 ing to this standard, "the term peat refers only to 

 organic matter of geological origin, excluding coal, 

 formed from dead plant remains in water and in 

 the absence of air. It occurs in a bog, swampland, 

 or marsh, and has an ash content not exceeding 25 

 percent by dry weight." The classification lists five 

 major plant types according to genesis and fiber 

 content. Percentages of fiber are based on oven- 

 dried weight at 105°C., not on volume. The five 

 types are: (1) Sphagnum moss peat, in which the 

 oven-dried peat contains a minimum of 66% percent 

 recognizable Sphagnum moss fiber; (2) Hypnum 

 moss peat, in which the oven-dried peat contains a 

 minimum of 33 Vs percent fiber, of which at least 

 half is Hypnum moss fibers; (3) Reed-sedge peat, 

 in which oven-dried peat contains a minimum of 

 331/3 percent fiber, of which at least half is reed- 

 sedge and other non-moss fibers; (4) Peat humus, 

 in which oven-dried peat contains less than 33 Vs 

 percent fiber; and (5) Other peat, which includes all 

 other forms of peat not classified in ASTM Desig- 

 nation D2607-69. 



As part of the research leading to the formula- 

 tion of this new classification, analyses were 

 made of 191 representative samples of peat sold in 

 the United States (Farnham, 1968, p. 89). Sphagnum 

 moss peat samples had the highest fiber contents 

 and generally the lowest ash content and pH. Also, 

 except for a few artificially dried materials, the 

 water-holdiTig capacities were well over 1,000 per- 

 cent. The hypnum moss peat samples were much less 

 acid but had slightly higher ash contents. Reed-sedge 

 peat samples differed in pH and ash contents and 

 had medium fiber contents and water-holding capaci- 

 ties. Peat humus samples were very low in fiber 



