That is a Texas infantry button. What markings are on the back? Depending on the backmark, that button could be anywhere from ths 1830's to the 1850's. Could you put a picture of the back up? That is an awesome find! Congratulations!
Im not exactly sure on the value but its a good bit if i remember right. A texas infantry button did make the banner here some time ago. Thats a rare button!
You need to start a new Thread on the buckle, note if there is any designs and/or lettering on it (front and/or back) and if so, good pics showing these.