Zultanite (gem-quality color-change diaspore) has perfect cleavage on the {010} crystallographic plane. This is the dominant durability constraint for the gem: a sharp impact aligned with that plane can cleave the stone cleanly. Master cutters orient the table facet to keep the cleavage parallel to the girdle (not the table) so daily wear distributes stress along the strong directions, not across the weak one.

The measurement

Crystallographic axis identification + impact direction analysis is the standard method documented in laboratory reference texts. Diaspore-specific values are documented across the property guides; this entry focuses on the practical implications.

Implications for buyers and graders

The value above is part of the verified mineralogical baseline editors apply when grading or authenticating a stone. Discrepancies from this baseline are documented case-by-case in laboratory reports and should be flagged before transaction.

Where this fits in the larger archive

See the related property guides for adjacent measurements and the cluster-support articles for practical applications.