Idrialite

Idrialite was first described in 1832 for an occurrence in the Idrija region west of Ljubljana, northwestern Slovenia,[4] mixed with clay, pyrite, quartz and gypsum associated with cinnabar.[2]

It also occurs at the Skaggs Springs location in Sonoma County, in western Lake County, and in the Knoxville Mine in Napa County, California.[2] It has also been reported from localities in France, Slovakia and Ukraine.[4]

In the Skaggs Springs occurrence, the mineral occurs in a hot spring area of the Franciscan formation, around a vent in the sandstone that gave off inflammable gases. The mineral was described in 1925 and named "curtisite" after the local resident L. Curtis who called attention to it.[9][10] The crystals are square or six sided flakes, 1 mm in diameter, yellow to pistachio green in transmitted light. It is associated with opaline silica, realgar (arsenic sulfide) and metacinnabarite (mercuric sulfide), which had been deposited in that order before it.[10]

The Curtisite variety is only slightly soluble in hot acetone, amyl acetate, butanol, petroleum ether. The solubility is 0.5% or less in hot carbon bisulfide, carbon tetrachloride, chloroform, diethyl ether, or boiling benzene; about 1.5% in toluene, about 2.5% in xylene, and over 10% in hot aniline. The material purified by repeated recrystallization melts at 360-370 C while turning very black. It sublimes giving very thin iridescent colors.[10]

Raman spectroscopy studies indicate that it may be a mixture of complex hydrocarbons including benzonaphthothiophenes (chemical formula: C₁₆H₁₀S) and dinaphthothiophenes (chemical formula: C₂₀H₁₂S).[11]

Curtisite and idrialite have been found to be unique complex mixtures of over 100 polyaromatic hydrocarbons (PAHs) consisting of six specific PAH structural series with each member of a series differing from the previous member by addition of another aromatic ring. The curtisite and idrialite samples contained many of the same components but in considerably different relative amounts.[6] [12]

The major PAH constituents of the curtisite sample were: picene (a PAH with 5 fused benzene rings), dibenzo[a,h]fluorene, 11H-indeno[2,1-a]phenanthrene, benzo[b]phenanthro[2,1-d]thiophene, indenofluorenes, chrysene, and their methyl- and dimethyl-substituted homologues; the major components in the idrialite sample were higher-molecular-weight PAH, i.e. benzonaphthofluorenes (molecular weight 316), benzoindenofluorenes (MW 304) and benzopicene (MW 328), in addition to the compounds found in the curtisite sample.[6]

Curtisite is also associated with small amounts of a dark brown oil, that appears to be responsible for some of the yellow color and most of the fluorescence, and can be separated by recrystallization.[10]

Based on the composition, it was conjectured that the compounds were produced by medium-temperature pyrolysis of organic matter, then further modified by extended equilibration at elevated temperatures in the subsurface and by recrystallization during migration.[7]

When distilled, it produces the mineral wax idrialin.[13][14]