Black Kyanite

Black kyanite is the same mineral as blue kyanite (Al₂SiO₅) but with higher concentrations of iron and graphite that produce the dark color. It shares blue kyanite's remarkable property of directional hardness - softer along the blade length (4.5) and harder across it (6.5-7).

What makes black kyanite visually distinctive is its habit: it frequently grows as fan-shaped or broom-like aggregates of radiating blades, sometimes called 'witch's broom' formations. These fans can spread 10-15 centimeters across, with thin black blades radiating from a central point in a dramatic spray pattern.

Black kyanite forms under the same high-pressure metamorphic conditions as blue kyanite - in aluminum-rich rocks subjected to intense tectonic pressure. The iron and graphite that produce the dark color were present in the original sedimentary rock before metamorphism.

Black kyanite is identified by its dark blue-black bladed crystal habit, directional hardness (4.5 along, 6.5 across), and characteristic fan-shaped aggregates. The blade habit with variable hardness is diagnostic.

Distinguish from black tourmaline (rounded triangular cross-section, uniform hardness), hornblende (different cleavage angles), and actinolite (different crystal system). The directional hardness test is definitive: if a dark blade mineral can be scratched by a knife along its length but not across its width, it's kyanite.