What is "sulphur rock"

Population (2000): 421
Housing Units (2000): 178
Land area (2000): 1.281165 sq. miles (3.318202 sq. km)
Water area (2000): 0.000000 sq. miles (0.000000 sq. km)
Total area (2000): 1.281165 sq. miles (3.318202 sq. km)
FIPS code: 67730
Located within: Arkansas (AR), FIPS 05
Location: 35.752009 N, 91.501807 W
ZIP Codes (1990): 72579
Note: some ZIP codes may be omitted esp. for suburbs.
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