Colour-Change Diaspore — How the Colour Shift Works

Colour-change diaspore shifts from kiwi-to-sage green in daylight to champagne, gold or raspberry-pink under incandescent or candlelight. The effect — the alexandrite effect — is caused by trace elements in the crystal, not by any treatment, and is strongest in cleaner, larger, well-cut stones.

What you are actually seeing

The stone’s colour does not change; the light does. Daylight and fluorescent light are weighted toward the blue-green end of the spectrum; incandescent bulbs and candlelight are weighted toward red. Diaspore’s trace-element chemistry gives it an absorption pattern that sits right at the balance point, so the colour you perceive tips one way or the other depending on which light dominates. This reversible, illuminant-driven shift is the alexandrite effect, named after the chrysoberyl variety in which it was first described.

The chromophores

The shift is driven by trace elements — chiefly manganese, with iron. (The precise spectroscopic mechanism for Türkiye diaspore is documented in peer-reviewed work; we describe it in general terms here rather than overstate the detail.) Manganese-bearing material also shows strong pleochroism — different colours along different crystal axes — which is a separate effect from the day-to-night colour change and is why the same stone can look subtly different as you rotate it.

Colour change vs pleochroism

These two are easy to confuse. Colour change depends on the light source and is seen as you move the stone between daylight and lamplight. Pleochroism depends on the viewing angle and is seen as you rotate the stone in one fixed light. Colour-change diaspore shows both.

How to observe it properly

• Look at the stone in two lights: near a window in daylight, then under a warm incandescent bulb or candle.
• Give your eyes a moment to adjust between lights.
• Judge the strength of the shift, not just the prettiness of one colour — a vivid, obvious change is worth more than a faint one.

Read on for how the colour change factors into buying and authenticity.