I'm not an expert but the metal bit with the hole...sorry, I don't know the technical name, tells me it's older...it's an odd looking button....1600's? From my limited knowlege...curious to know if you were detecting in an area where you might find something that old...
...with no connection to a military or militia unit these buttons are generally and collectively known as ball buttons and are usually found at sites dating from the early to mid 1800s
It's a civil war period dragoon style 3 piece "ball" or "zouave" style button. Used by military and civilians alike, they abound on some 1850-70's sites. That style button first came into use by about 1835. They are always a good find.
Tencents, if you aren't familiar with the Zouaves, they were soldiers, who stood out because of their lavish uniforms and dress. The Union or Federal Zouaves dressed in red baggy trousers, white gators, or leggings, and most wore ornate vests, and wore a tassled fez for headgear, or a variation of headgear adopted by their particular unit. These uniforms were of foreign design and made these soldiers stand out. Most of the Federal Zouaves consisted of Firemen which had enlisted and became soldiers. Col Elmer Ellsworth was a young and upcoming officer in the Union Army. He formed and trained the New York Fire Zouaves. Col Ellsworth was a personal friend of President Abraham Lincoln and was said to be the first Union officer to be killed in the Civil War after cutting down a Confetrit flag that was flying above an Inn in Alexandria, Virginia. Col Ellsworths personal guard returned fire and killed the Innkeeper who had shot and killed his Col. If you have ever seen this pic. of the soldier who killed the Innkeeper, he is dressed in his Zouave uniform. The Confetrits had Zouaves too, and a number of them were from Louisianna and were known as "Wheats Tigers", or Col. Wheat's Zouves. A lot of these Zouaves were of French and Creole origin. Although not quite as flashy as their Northern counterparts, they too sore the foreign dress uniforms and were known to be very tough and well trained soldiers.