Midnight — The Trade Term for Inky Australian Sapphire
Midnight — The Trade Term for Inky Australian Sapphire
Very dark blue corundum, principally from the Queensland and New South Wales basalt fields
Midnight is a trade descriptor for blue sapphire of very dark tone, approaching inky or near-black character, in which the underlying blue hue is visible only when the stone is held to a strong light source. The term is descriptive and unstandardised; it is used by Australian and international dealers to describe a colour space that sits at the dark end of the sapphire tonal scale, well past the medium-dark of conventional fine blue and into a region where transparency and brilliance are sacrificed to depth of colour.
Origin and cause
Midnight sapphires originate principally from the basalt-related deposits of eastern Australia — the Anakie field in central Queensland and the New England district of New South Wales — and from related basalt occurrences in Thailand, Cambodia, Laos, and parts of China. Basalt-related sapphire is characteristically high in iron, and the dense iron content drives both the deep blue colour and the tendency toward strong tonal saturation. Where iron is exceptionally high and the stone has not been heated to drive off the silk that absorbs additional light, the resulting colour can become so dark that the stone reads as black under all but the strongest illumination.
Heat treatment can lighten the most extreme midnight material somewhat by dissolving silk and improving transparency, but the underlying iron content remains and limits how far the tone can be opened. Stones that survive aggressive heating with their colour intact are typically the most valuable in the midnight category.
Trade position
Midnight stones generally trade at a meaningful discount to medium-dark blue sapphires of equivalent size and origin. The reason is straightforward: the dark tone reduces the perceived colour and the brilliance the stone returns face-up, both of which are the primary value drivers in the broader sapphire market. The market for midnight material exists, however, and serves customers who specifically want a dramatic, near-black gemstone with subtle blue flash visible at certain angles, or who are working within a design context where a dark stone is preferred to a bright one.
The term should not be confused with black star sapphire, which is opaque to near-opaque material with dense rutile inclusions producing asterism in cabochon — a different optical phenomenon and a different commercial category.