corundum, Australia.12, inclusions.5, gems

Examination of a parcel of approximately thirty blue Australian sapphires reveals exceptionally closely spaced growth zoning that can resemble the fine striations associated with synthetic corundum. The stones, submitted by John Fleming of New Zealand, attracted attention because their growth bands were of a similar order of size to those seen in synthetic material. Although the observed striations showed no curvature, this distinction alone was insufficient to resolve their origin immediately: in small stones fashioned from a large synthetic boule, curvature may be inconspicuous, particularly under strong magnification. The report therefore identifies a potential difficulty in interpreting fine zoning when only a limited portion of a growth structure is visible within a faceted stone. Further microscopic examination disclosed convincingly hexagonal zoning in some specimens, together with healed fractures, providing additional evidence for their identification as natural sapphires. Photomicrographs illustrate both the closely spaced straight bands that initially prompted concern and the more diagnostic hexagonal pattern found during the subsequent investigation. Other observations document the physical and optical characteristics of the parcel. Testing in Clerici solution showed the stones to have densities slightly greater than that of a reference sapphire with a density of 3.995, although individual numerical determinations were not reported. Refractive indices measured with a Rayner refractometer in sodium light ranged from 1.765 to 1.780. Dichroism was pronounced, producing green and purple shades of the blue body colour. Examination between crossed nicols revealed neither strain nor twinning, and no further features of particular interest were recorded. The stones were described as richly blue but somewhat dark. The principal contribution is the documentation of unusually fine natural growth zoning whose scale and appearance approach those of synthetic corundum. Its diagnostic implication is that closely spaced striations should be assessed through their geometry and associated internal features, with particular attention to the possibility that a small field of observation can conceal curvature. The note offers an observational account of this identification problem rather than an explanation of the geological conditions responsible for the exceptionally narrow zones.