Currency devaluation
The diamonds purchased can be resold throughout the world, even in stronger currencies.
Production oligopoly
The production of diamonds is in the hands of a few large international players, who control the offer avoiding price declines.
Bank default
Since they are not tied to any bank, there is no risk of losing the funds held at the failed Credit Institute.
Political instability
The diamond is a movable good and can be transported elsewhere without excessive effort, if the political situation requires it.
Fungibility
The diamond, as a fungible asset, is the property of whoever owns it (like any banknote), or “good faith possession means title”.