octahedron and octahedron. From Sudafrika.
No. 3. Diamond in the form of octahedron with intersections.
No. 4. Diamond from Brazil.
No. 5. Diamond from Kimberley.
No. 6. Diamond from Brazil.
No. 7. A made or twin crystal, showing its formation from an octahedron with curved edges.
Some crystals of diamonds have their surfaces beautifully marked with equilateral triangles, interlaced and of varying sizes (Fig. 15). Under the microscope these markings appear as hollow depressions sharply cut out of the surrounding surface, and these depressions were supposed by Gustav Rose to indicate the probability that the diamonds had at some previous time been exposed to incipient combustion. Rose pointed out that similar triangular striations appeared on the surfaces of diamonds 87
