Carnelian

This variety of chalcedony with colors between red, brownish red, and orange red was said to have the power to drive away evil and bring good luck.

Carnelian was supposedly the right stone for those with weak or timid voices, because it could give them courage to speak boldly and well.
It was also said to protect against the envious, and was responsible for making sure the desires of its wearer were gratified.

The popularity of carnelian in the Islamic world may be due to the fact that Mohammad himself wore one as a signet ring.

Carnelian of a dark or brown shade, is called Sard. Sard was thought to provide protection against incantations and sorcery, and was believed to sharpen the wits, rendering the wearer fearless, victorious in his endeavors and happy.

Sardonyx consisting of bands of sard and black and white layers, alternates with peridot as the birthstone for the month of August.