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rich in magnesium
a black mechanical pencil (it has an eraser)
Brown calcite is an interesting challenge to students who have been introduced to common white or light gray calcite
In this case it is often considered a cryptocrystalline variety of quartz like chalcedony and is thought of as a mineral
In some years none are found at all
galena - teaching student specimens of the primary ore of lead with attached matrix - Talsint (?) Morocco - Unit of 5 specimens rich in magnesiumGalena PbS Galena is a very common metallic sulfide. It often occurs in cubic crystals and has good cubic cleavage. It is practically the only source of lead, which is used in huge amounts in storage batteries and in shielding from radioactivity. Galena is the Latin name for lead ore. Galena is easily identified by students by its density, metallic luster and its cubic cleavage. Not cleaved into rectangular blocks, though they show cubic cleavage,
