9 and 10, p. 1096. It is found in vuggy masses of barite, in barite and calcite veins, and in the silty, carbonaceous limestone host. Gillulyite has a deep-red color and a red streak. It is translucent but tarnishes rapidly to a darker red or blue. Gillulyite forms very small, slender, prismatic crystals and has one perfect cleavage that is obvious on all specimens.
Associated minerals are barite, calcite, orpiment, realgar, lorandite, raguinite, and pyrite.
Gillulyite was named in honor of the late James C. Gilluly, author of the U.S. Geological Survey Professional Paper 173, Geology and Ore Deposits of the Fairfield and Stockton Quadrangles, Utah . 9 and 10, p. 1096. Utah Geological Association Publication, no. 18, p. 78. Mcalpineite was named for this California mine. At the Centennial Eureka mine, Mcalpineite was found as a coating in pore spaces in decalcified, brecciated brown-grey limestone boulders located in the mine dump.