ARTSMITHITE, A NEW Hg1+-Al PHOSPHATE-HYDROXIDE FROM THE FUNDERBURK PROSPECT, PIKE COUNTY, ARKANSAS, U.S.A.

Abstract

Artsmithite, with the general formula Hg 1+ 4 Al(PO 4 ) 2-x (OH) 1+3x (x = 0.26), is monoclinic, C2/c, with the following unit-cell parameters measured on a single-crystal X-ray diffractometer: a 17.022(5), b 9.074(2), c 7.015(2) Å, ␤ 101.20(1)°,V 1062.9(8)Å 3 ; a:b:c 1.8759:1:0.7731,Z = 4.The strongest eight lines of the X-ray powder-diffraction pattern [d in Å(I)(hkl)] are: 8.326(100)(200), 4.739(50)(310), 4.166(40)(400), 2.979(80)(202), 2.952(50)( 402), 2.784(80)(600), 2.660(75)(330) and 1.755(50) ( 732,640, 204).The mineral occurs as a colorless-to-white matted nest, approximately 3 ϫ 1 mm in size, of randomly scattered fibrous to acicular crystals at the Funderburk prospect, Pike County, Arkansas, U.S.A. Associated minerals on the holotype specimen are quartz, goethite, dickite and cinnabar; other minerals reported from the locality include barite, calcite, calomel, eglestonite, fluorapatite, galena, livingstonite, native mercury, metacinnabar, montroydite, perhamite, pyrite, siderite, stibiconite, stibnite and terlinguaite.Artsmithite is a secondary phase most probably formed from the breakdown of primary cinnabar and apatite.Individual needles are elongate [001], colorless, transparent, with a length-to-width ratio in excess of 100:1, and they average about 0.5 mm in length.Artsmithite is vitreous, with an off-white to cream streak, no obvious cleavage, irregular fracture; it is nonfluorescent, and the needles are flexible.D(calc.) is 6.40 g/cm 3 for the formula inferred from the crystal-structure analysis.It is biaxial positive, and all indices of refraction exceed 1.80; 2V (meas.)60°; r < v, distinct; length slow with Z ≈ c.An electron-microprobe analysis gave Hg 2 O 78.28, Al 2 O 3 5.02, P 2 O 5 11.39, H 2 O [1.63], total [96.32]wt.%.The empirical formula, derived from the results of the crystal-structure and electron-microprobe analysis, is Hg 1+ 4.00 Al 1.05 P 1.71 O 8.74 H 1.78 , on the basis of O = 8.74 and (OH) = 1.78 (from crystal structure).The infrared-absorption spectrum shows bands for structural (OH), adsorbed (H 2 O) and phosphate.The name honors Arthur E. Smith, Jr., of Houston, Texas, who collected the mineral specimen in 1995.