Some Controversial Notes on the Diamond. 
129 
shells, are often found. The ori£?inal whole shells evidently held inclusions 
nearly as large as themselves, then broke and the inclusions fell out. In 
some analogous cases inclusions have pushed holes through opposite faces 
of diamonds, leaving natural diamond beads. 
Sometimes portions of such shells are found containing a material not 
unlike cement iu appearance. I have a specimen whose dimensions are 
6'5 X 5-5 X 2 5 mm., the shell being no more than a millimetre thick. The 
specific gravity of the specimen is 3*56, indicating a denser material than 
diamond though softer — possibly diamond containing some impurity. Frag- 
ments of rounded specimens are occasionally found in which the cement and 
the transparent diamond are in alternate layers like the coats of an onion. 
Whatever the nature of this cement it sets up more strain than the thin 
diamond shells can resist.* 
(3) Some experiments were made with a clouded biown Wesselton 
diamond of about three carats weight, much flawed and somewhat strained 
internally, with the object of increasing the strain or extending the cracks. 
These experiments consisted of heating the diamond in a test-tube in the 
flame of a spirit lamp, and of boiling it in water. The result was negative, 
and to all appearance the diamond is in the same condition now as it was 
before it was experimented upon many months ago. 
(4) A nice rounded octahedron from Dutoitspan, of about three-quarters 
carat, in my collection, had a beautiful, slightly flawed smoky corner — just 
the sort of specimen to explode spontaneously according to the 40tli Article. 
It was lieated in the test-tube until the glass became soft, and was then 
placed under the receiver of a good air-pump and subjected to a considerable 
exli;iustion of air. The flaw may have developed slightly under this drastic 
treatment, 
3. Deductions. 
The generalisation here proposed is that owing to the small coefficient 
of expansion of diamond almost any inclusion will set up a state of strain in 
* Sorby and Butler (' Proc. H.S.,' 1869) noticed that foreign inclusions exerted 
pressure on the surrounding- diamond. And tliey say, "We, however, do not imagine 
that the crystals [inclusions] have increased in size, but that probably they have 
prevented the uniform contraction of the diamond, which must have been very 
irregular even wdien no such impediment Avas present." This suggestion ignores 
the contraction of the inclusion. There is something remarkably like hailstones 
in the structure of these specimens, and no doubt they have been formed like 
hailstones by alternate phases of crystallisation and accretion. Their characteristics 
must have an important bearing upon any rational theory of the genesis of the 
diamond. Covild the old philosophers, who taught that precious stones were petrified 
ice, have seen such things they could have claimed a very decisive corroboration 
of their doctrine ! "Other minerals, as fluor-spar, apatite, idocrase, heavy spar and 
calc-spar, disclose a similar structure by bands of different colours. A growth 
rendered intermittent through the deposition of a thin layer of foreign matter is thus 
developed" (A. F. Heddle, ' Ency. Brit.,' 9th ed., 1878, Art. 'Mineralogy '). 
