Sphene

Sphene was a precious stone that came in many colors and, like scapra, was easily worked by unskilled cutters.

Description
Sphene was a soft, brittle gemstone that came in shades of yellow to deep green with a fine emerald green as the most prized hue. Sphene crystals could be cut into beautiful, sparkling, faceted gems of small to medium size. A typical specimen had a base value of 500 gp.

Powers
Wearers of this stone may not have known it, but they were much less likely to be hit by lightning or lightning-like spells or effects. And if they were struck, the damage not as bad as it might have been.