Orthoclase is a transparent yellow feldspar resembling citrinequartz or yellow beryl, found primarily in Madagascar. It has a Mohs hardness rating of 6-6.5, so is most suitable for collectors or for pendants, earrings and pins.
I love GemSelect, personally. I browse their site almost daily to see all the new stones available. Their selection is pretty amazing. The quality isn't always the highest and the cut of the stones isn't always perfect. But for the price, and if you look hard enough, you can find a real gem, so to speak.