Stone Beads: Santa Rita Green and Purple
April 11, 2012
This Moon I have been carving stone beads from pebbles that I collected in Sycamore Canyon and other canyons in the Santa Rita Mountains. Eventually I want to make enough for a necklace. I have a fairly efficient system for cutting the blanks, drilling holes, carving, hand-sanding, and polishing. Even so, it’s a slow process, averaging one finished bead a day. It’s fun to watch the strand grow. It’s acquired a “Green and Purple” color theme, partly inspired by the rocks themselves and partly by the endemic Santa Rita prickly pear cactus (Opuntia santa-rita), which is pale grayish-green in the summer and turns a distinctive mauve color in winter. Three of the new beads are shown below. All are slightly softer than agate and take a soft polish rather than a mirror shine, even when diamond powder is used. At left is a bead made of diopside (a green pyroxene) and calcite, sometimes called “calcsilicate rock”. It is from a skarn, a special type of contact metamorphic rock that is produced when granitic magma intrudes limestone or marble. In the center is a volcanic rock that has been extensively altered to clays and hematite, so its original composition is unknown (it’s from the outcrop pictured below). At right is an altered and slightly metamorphosed rhyolite; the pistachio-colored mineral is epidote and the dark green veins are diopside. Rhyolite is a light colored volcanic rock which is equivalent to granite in composition; it is the main rock type of the Santa Ritas but comes in a wide variety of colors and textures.
Here’s an outcrop of altered and weathered purple volcanic rock with a vein of epidote (yellowish-green), chlorite, and diopside (bluish-green) exposed on a weathered surface.
Here’s the Santa Rita prickly pear in midwinter, growing wild in Chino Canyon. The green prickly pear in the center of the photo is a more common species, Opuntia engelmanii.