Sulphate of Barytes

The upper fragment is in the form of the nucleus, or an upright parallelopiped; and as the faces are the same with the primitive, it is placed with the upright faces on a line, to show the refraction is not double in that direction: and it is to be observed that it requires a large depth of crystal to see the refraction through the other faces without the assistance of a lens. The flaws show the prismatic tints, like other laminated crystals; this shows the depth of the flaw, and it is so sufficiently elastic that we can, by pressure, dilate the prismatic hues, so that one or two sets may take place of the 5 sets represented.

We received this specimen from Durham, by favour of Messrs. Harriman and Oliver, some few years since—but did not know how valuable it was until lately—having now discovered that it contains many small drops of water or some other liquid in little hollows, which as far as we know have never been discovered in any other substance except quartz, or rock crystal.

The lower one is another fragment with a curious pearly appearance, and has somewhat the appearance of sulphate of lime or gyps, but may be readily discovered by the weight.