This is a beautiful, polished piece of petrified palm wood (Palmoxylon) from Eden Valley, Wyoming. One face has been polished to a mirror like finish allowing the much of the inner wood detail to be easily seen. It was cut from the end of a log, so it varies in thickness up to 1.1" thick.
Palm wood has lacks the familiar, circular grain pattern of wood. This is due to the structural differences between palm and other woods. Palm tree trunks are a cluster of vascular tissue surrounded by supportive tissue, where as true woods have these tissues arranged in concentric rings. This absence of rings gives petrified palm wood its distinct look.
Petrified palmwood includes a group of fossil woods that contain rod-like structures within the regular grain of the silicified or agatized wood. Depending upon the angle at which they are cut, these structures show up as spots, tapering rods, or continuous lines. The rod-like structures are sclerenchyma bundles that comprise part of the woody tissues that gave the wood its vertical strength.