342 Mr. D. Forbes on Evansite, a new Mineral Species. 



preliminary blowpipe examination immediately confirmed this 

 opinion by proving the absence of silica in any quantity, and 

 indicating the presence of phosphoric acid; and consequently I 

 was more disposed to regard it as hydrargyllite or Gibbsite. I 

 commenced, however, a systematic examination of the mineral, 

 but my sudden departure and prolonged absence in South Ame- 

 rica has prevented my having had an opportunity of making the 

 results public until my recent return. 



The physical characters of Evansite are as follows : — Amor- 

 phous and without trace of crystallization ; reniform or botryoi- 

 dal ; colourless or milk-white, and sometimes faintly tinged with 

 yellow or blue, and occasionally presenting iridescent hues; streak 

 white ; translucent to semi-opake. Lustre, vitreous or resinous ; 

 splendid and waxy internally ; very brittle. Fracture semicon- 

 choidal and shining. 



Hardness 3*5 to 4, scratching calc-spar with facility but not 

 fluor-spar ; one fragment, however, was found, to leave a faint mark 

 on fluor-spar. 



Specific gravity. Several determinations were carefully made, 

 and precautions were taken to expel all air from between the 

 lamina? of the mineral by using boiling distilled water and allow- 

 ing it to cool down to the temperature of 60° Fahr. ; the results 

 w r ere as follows : — 



1. Using 28-51 grains of the translucent colourless mineral 

 in small fragments, the loss in water was found to be 15*59 

 grains, and the consequent specific gravity 1*822. 



2. With 13*686 grains similar to last, the loss in water was 

 7*31 grains, and the calculated specific gravity consequently 1*872. 



3. With 12*87 grains of faint-yellow-coloured mineral in frag- 

 ments, the loss obtained was 6*13 grs., and the consequent spe- 

 cific gravity w r ould be 2*099. 



4. When 18*793 grains of semiopake mineral in one piece 

 was immersed under water, it lost 9*55 grains, and consequently 

 had a specific gravity of 1*965. 



The mean of these four determinations will give 1*939 as the 

 specific gravity of Evansite. 



The behaviour of this mineral before the blowpipe was found 

 to be as follows : — 



In a closed tube it immediately evolved water, decrepitated, 

 and, on continued application of heat, gave off more w T ater and 

 remained behind in the form of a milk-white powder. On test- 

 ing, the water evolved did not show any reaction with Brazil 

 wood, red or blue litmus, or turmeric test papers. 



In an open tube the same reactions were observed. Heated 

 between platinum points it very slightly swelled out, became of a 

 milk-white colour, and presented, when viewed through the glass, 



