Stick agate is a pseudomorph (from the Greek “false form”) when the original crystal form of one mineral is occupied by another, chemically or a structurally different species. Most of the pattern that you see in the stone is Aragonite that has been replaced by Chalcedony.  The triangular shapes you see are a quartz pseudomorph of Aragonite.

The stone is surrounded with Argentium sterling silver wire, which is sterling silver with a trace of germanium and no nickel.  The Argentium is more tarnish resistant than plain sterling silver and some people that are allergic to sterling silver have found Argentium is an acceptable alternative.