What is a zeolite occuring in groups of glassy acicular crystals, and in masses which often have a radiated structure. It is a hydrous silicate of alumina and soda called?

natrolite — A zeolite occuring in groups of glassy acicular crystals, and in masses which often have a radiated structure. It is a hydrous silicate of alumina and soda. (Webster's 1913.)

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