military button?

Hi all, new to the site and hoping to get some ID help. I did browse through a bit and saw that there seem to be some members with a lot of knowledge about Horstmann buttons. From the backmark I am assuming this one is circa 1890s based on my reading but I am more curious to know if anyone...

My son found this last week while hiking up Gibraltar. It looks like an old military button. I tried searching online to identify it, but couldn’t find a match. Does anyone here know what it might be or where we could look? Thanks in advance! PS, the button is round not oblong, it looks a bit...

Found button detecting.

Dug this old button yesterday and cannot find it anywhere. I have search many relic sites and also military sites for older buttons. I wonder if anyone has seen a button like this one.