tuff - gritty gray-white uniform welded volcanic ash - - UNIT OF 5 SPECIMENS

Description

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Gritty gray-white tuff - teaching student specimens - Unit of 5 specimens
This is a gritty gray-white tuff - a welded volcanic ash. It has almost no darker clasts and might challenge students who expect to see broken fragments of rocks that have been torn from the vent included in the welded ash.
Many tuffs contain angular clasts (from the Greek
klastos
= broken). As the ash was being blasted out of the vent, fragments of other rocks were being torn loose and blasted out with it. Angular clasts make a tuff relatively easy to identify and to separate from a rhyolite.
Both rhyolite and tuff are derived from a magma with the same composition as granite. Tuffs are variable in color as is rhyolite, but rhyolite but is entirely crystalline, though the crystals are often difficult to see without a 10x lens.
An adjacent less welded layer of this tuff, a sedimentary pumice lapilli tuff, was mined from 1919 to around 1960. It was used as the polishing agent in toothpaste, in oil-absorbing compounds, and in acoustical plaster, cleaning compounds, wood fillers and in paint. The bed dips steeply to the west and the miners simply followed it down. Collected at the former Calsilco mine at Last Chance Canyon, Kern County, California.
If you are a science or earth science teacher purchasing this as  teaching specimens for your class, this should be compared with other silica rich volcanic igneous rocks, tuff breccia, pumice (which is so full of entrapped gases that it floats in water) and rhyolite (extruded as lava) and with silica rich plutonic igneous granitic rocks. A tuff breccia will have larger fragments (clasts) of various igneous rocks than does this tuff. Tuffs, rhyolite, pumice  and granite all have the same silica-rich composition
We really don't like the tiny finger nail-sized specimens offered to students, as we feel these are too small to see rock textures and too small for examining the identifying characteristics of a mineral. We collect these specimens so that five specimens, or possibly six, will fit in a small flat rate box, and we keep the price low, as we know these will be used in a classroom. For teachers we count like a baker and a dozen is more than 12, since you will always need a few spares.
If you are a teacher, let us know.
You are buying a unit of five student specimens.
The photo is representative of what we ship.
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Ships in a small Priority Mail flat rate box unless combined with other purchases. We always combine shipping to get your purchase to you at the lowest cost. We do not charge for handling. We refund any overpayments on shipping beyond our actual cost. A second unit moves the shipment into a larger box. We can generally ship 4 to 5 student units or a number of hand specimens in that box with no further increase in postage.
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