Heating value of borehole samples of lignite ranges from 500 to 1,000 Btu/lb within short distances. Much of this variation is caused by (1) weathering at shallow depth, resulting in a decrease in heat value, and (2) loss of moisture because of improper handling of the sample, resulting in an increase in heating value. Aside from these factors, the petrographic composition of lignite is the most important parameter that ultimately controls its heating values (assuming geologic history is the same after the peat stage). Chemical analyses of hand-picked pure maceral material exhibit considerable variation in elemental composition and heating values. On an as-received basis, the heating values of resinite and huminite (vitrinite) are 16,000 Btu/lb and 7,500 Btu/lb, respectiv ly. The hydrogen and carbon contents are 10 % and 80 %, respectively, for resinite and 5 % and 70 % for huminite, calculated on a dry, ash-free basis.

Lignite mined near Larson, Burke County, North Dakota, contains resinite particles with a diameter up to 0.5 in. Published data (212 samples) indicate that the average heating value of this lignite is 460 Btu/lb more than the average value for all lignite in North Dakota (7,280 versus 6,820 Btu/lb). A presence of 5 % resinite could account for this difference in heating values.

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