270 Hillebrand and Schaller — Mercury 



Terlinguaite. 



Monoclinic prismatic (holohedrai), a : 1> : c= 1*6050 : 1 : 

 2-0245 (Schaller), /3-74 23'. Of the 133 forms observed 102 

 are new. Crystals often extended in one direction and also equi- 

 dimensional. The largest crystal measured 16XlX4 mm , though 

 faces over a centimeter broad are sometimes to be seen. Also 

 occurs in powdery form impregnating the earthy gangue, to 

 judge from the greenish color of some specimens of ore, and 

 perhaps in a similar state admixed with eglestonite, in which 

 case its identification is at least difficult. Much confusion 

 seems to exist as to the original color of terlinguaite before it has 

 been exposed to light. Moses writes of it as " sulphur-yellow 

 with a slight greenish tinge, very slowly darkening on exposure 

 to an olive green," but Mr. Hartley, in reply to our inquiry, 

 wrote that the terlinguaite crystals were green ere they were 

 touched by the sunlight, but that most of the terlinguaite occurs 

 as a yellow powder changing to green. Sometimes brown 

 crystals are seen and occasionally the green and brown colors 

 appear in the same crystal. When brown they are difficult to 

 distinguish at sight from eglestonite in one of its transitional 

 color stages. Some of our earthy specimens that were yellow 

 at first turned greenish on exposure and presumably contained 

 terlinguaite. Beautiful spots of emerald-green reflected light 

 appear when the crystals are examined with a lens as they 

 occur on the specimen. If at times originally yellow the min- 

 eral is not in that state always distinguishable from kleinite, 

 and perhaps not from eglestonite or even from the orange-red 

 form of montroydite. 



Streak yellow, turning greenish gray in light. Transparent 

 or nearly so. Luster, brilliant adamantine. Cleavage, perfect 

 1 101}. Brittle to subsectile. Hardness 2-3. Density, 8*725 

 (Moses). 



The effect of heating crystals in a closed tube differs some- 

 what according as this is done slowly or quickly. When 

 quickly done there is violent decrepitation, continuing till the 

 mineral has volatilized, the substance turning red-brown or 

 almost vermilion in color (orange-yellow cold) and much of 

 the resulting powder being projected up onto the sublimate of 

 calomel and mercury above the assay. Eventually there is 

 complete volatilization. With slow heat decrepitation is hardly 

 noticeable. With the first burst of calomel sublimate there 

 appears a little mercury, but then only calomel so long as there 

 is any chlorine left in the residue. Sometimes at the last, 

 when the flame is removed, brilliant short red needles of mer- 

 curic oxide form on the warm glass by recombination of some 

 of the mercury vapor and oxygen. 



