Abstract
An unusual occurrence of analcime has been found at Coffin Butte, Benton County, Oregon. Trapezohedrons of analcime are arranged in spheroidal clusters with hollow centers. Natrolite occurs as acicular prismatic crystals completely enclosed within the analcime. The arrangement of the natrolite indicates that it originally radiated from the now hollow centers of the clusters.
The spheroidal clusters, which often appear only as rings of crystals, are not due to cyclic twinning as has been suspected, but the grouping probably has been controlled by the radiating structure of the natrolite. The steps in the development of a spheroidal arrangement of this type can be seen from a study of perched crystals. With analcime perched on nalrolite as a starting point, further growth of the analcime and removal of the unprotected natrolite would produce spheroidal clusters of analcime such as were found at Coffin Butte.