The modern birthstone for August is Peridot and I have to say I love it to bits.
This necklace has a Lapis Lazuli star with little hanging Peridots on an oxidised silver chain.
Available from my shop here
The traditional birthstone is Sardonyx, I have just launched a new range featuring Sardonyx and lava. It is still waiting to be loaded to the website though
The cabochon birthstone is Carnelian, a pretty orangy red colour as seen here