This is actually a really good piece for the locale. This dam, near metro Phoenix in a Mountain park to the north, was the site of a remarkable find of zeolite minerals. Such specimens are now very hard to find on the market and this is the best natrolite from there, I have had. It features a sparkling, spherical cluster of natrolite needles, to 2 cm in size. The matrix probably is clinoptilolite, in basalt. From the well-known Tucson collection of 40-year collector, Harold Urish.