This is a Moctezuma Agate with tight white banding and a open inflow/escape tube. There two hairline fractures at the top and the bottom barely noticeable without magnification.
It has a mirror polish.
Moctezuma Agate
Estacion de Moctezuma
Chihuahua, Mexico
4.7 x 4.2 x 3 cm / 85 grams