This mystery’s rock
What a nice piece of agate! Very colorful. Based on the tip of the rock with the speckles and the curious back side of the piece, it may be a piece of agatized coral.
Agate is a form of quartz which is a silicate.https://en.wikipedia.org/wiki/Agate
I suggest taking it to a local geologist for further identification, if you are curious about a potential fossil story. Nice find!