Fibrous Analcime in Trap

Zeolite, formerly so called, is often found in trap, as if passing from opaque hyalite of Kirwan (see our Tab. 57.), at length leaving the spaces where it was first formed empty, and giving the stone the appearance of a scoria or basaltic lava. This is a red variety of basaltic trap, which has hyalite of a pebble-like appearance in one part. In some cavities it has partly fibrous zeolite; in others the zeolite appears in fine filaments, sometimes of a silky lustre, filling the holes like cotton or with loose threads, which are often scattered more or less in irregular bundles, somewhat radiating. The hollows which contain these are mostly lined with small crystals. These at first sight look like quartz, such as often sparkle in common flints, but if examined with a glass their structure determines what they are. See Tab. 59. and magnified figure at the middle and bottom of this plate.

We use the old term of zeolite, as being most familiar; at present it is synonymous with analcime.