ANALCIME PSEUDOMORPH AFTER ANALCIME AND NATROLITE

Analcime, also known as analcite, is a tectosilicate mineral that appears in shades of white, gray, or colorless. It is composed of hydrated sodium aluminum silicate and crystallizes in a cubic form, with the chemical formula NaAlSi2O6 · H2O. There are minor substitutions of potassium and calcium for sodium, and a synthetic variant containing silver, referred to as Ag-analcite, also exists. While analcime is typically categorized as a zeolite, its structural and chemical properties align more closely with feldspathoids. Although its crystal structure is generally considered isometric, slight angular discrepancies complicate its classification, with some truly isometric samples present. The subtle variations among samples have led to the consensus that multiple species names are unnecessary, making analcime a notable example of minerals that can exist in various crystal systems and space groups. The mineral was first identified by French geologist Déodat de Dolomieu, who referred to it as zéolithe dure, or hard zeolite, and it was discovered in lava formations in Cyclops, Italy. Analcime is recognized by the International Mineralogical Association and retains its status as a valid species.

Natrolite is a mineral species classified as a tectosilicate and is part of the zeolite group. It is a hydrated sodium and aluminum silicate with the chemical formula Na2Al2Si3O10·2H2O, and its type locality is Hohentwiel in Hegau, Germany. 

The mineral was named natrolite by Martin Heinrich Klaproth in 1803, with the name originating from the Greek word for soda, "natron," reflecting its sodium content, and "lithos," meaning stone. Informally referred to as needle stone or needle-zeolite, this designation highlights the typical acicular form of its crystals, which are often slender and arranged in divergent tufts. The crystals may also exhibit epitaxial overgrowths of natrolite, mesolite, and gonnardite in various configurations.