16 
BULLETIN NO. 32. 
and heated to boiling temperature on the hot water bath they become white 
and opaque, apparently losing water just as when heated in air. This insta- 
bility in the presence of water at 100 degrees would seem to indicate a low 
temperature of formation for the mineral and is in agreement with its mode 
of occurrence as crystals associated with and later than selenite lining vugs 
in the gypsum masses. 
CHEMICAL ANALYSIS AND COMPOSITION. 
The sample for analysis consisted of clear, transparent crystals and 
crystal aggregates which were carefully examined under a binocular micro- 
scope for intergrown or attached selenite. Many of the crystals examined 
showed inclusions of minute selenite crystals and as these have the same 
index of refraction as inyoite and are also clear and transparent, they are 
Figure 9. Graph showing water loss of inyoite on heating at increasing temperatures. 
very difficult to detect, so that in spite of the care exercised in selecting the 
material, analysis revealed the presence of about one per cent of selenite. 
The sample was crushed by impact to 80 to 100 mesh on a polished 
steel plate, using a flat-faced steel pestle, any grinding motion of the pestle 
being carefully avoided, owing to the possibility of loss of water. After 
thorough mixing, several portions were weighed out at once and the water 
determination started immediately. A half gram portion in a platinum 
crucible was heated in an electric oven at an initial temperature of 100 
degrees and weighed from time to time after cooling in a desiccator over 
sulphuric acid, the results being indicated graphically in Figure 9. In this 
case 30-66 per cent of water was lost in the first thirty hours at 100 degrees 
C. The temperature was then gradually increased as indicated on the 
graph, the oven being set so that these temperatures were never exceeded 
for the periods indicated, though there might be a fall of 2 or 3 degrees 
from time to time. At 109 degrees C., constancy of weight was attained 
after a loss of 32-46 per cent which four days additional heating failed to 
increase. It may be noted that this loss considerably exceeds that found 
