Rare blue Prehnite crystal cluster from the Merelani Tanzanite mines. The blue Prehnite from this locality is far less common than the yellow and displays a color change (two different shades of blue) in indoor versus outdoor lighting. The Prehnite is undamaged though there are some cleaves of Calcite on the left side. This is a great example I've held onto for about 10 years or so and also has small Sphalerite, Diopside, and even a bit of Tanzanite attached, along with the black Graphite.