Mr. Gregor on a native Arseniate of Lead. lgj 
quently exhibits on its surface the appearance of a partial de- 
composition. 
The red octaedral copper ore, and the copper into which 
that ore passes, are often intermingled with the crystals of 
this lead ore and inbedded in them. 
The colour of these crystals consists of a variety of tints of 
yellow. Some are of a beautiful wine yellow resembling the 
Brazilian topaz : this, in the greater number of specimens, 
passes into a delicate Isabella-colour : whilst, in other cases, 
we have the honey-yellow mingled with brown hues of dif- 
ferent intensities : so that we meet with crystals resembling 
dark brown sugar-candy, or common resin. 
Some of the crystals are beautifully transparent, whilst 
others possess this quality in part only, at their extremities, 
or in inferior degrees throughout their whole lengths. 
The external lustre in some specimens, is vitreous ; in others, 
resinous : but in some instances their surface is partially co- 
vered by tender and delicate filaments of a silky lustre. These 
filaments are sometimes found in a separate state loosely ad- 
hering to quartz ; and they form a variety of this fossil. 
The crystals vary as to hardness. The angular fragments 
of the most transparent are sufficiently hard to scratch glass. 
This mineral is easily reduced to powder, which has the ap- 
pearance of pounded resin ; it contracts a yellower tint by 
long exposure to the air. 
The specific gravity of the purest crystals, taken at the 
temp. 50° Fahrenheit, was 6.4 1. 
D d 
MDCCCIX. 
