Specific Gravity: Judging a Mineral by Its Weight in the Hand
Quick answer: Specific gravity is how heavy a mineral is compared with an equal volume of water. Quartz is about
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The Streak Test: Why a Mineral’s Powder Color Can Differ From the Mineral Itself
Quick answer: The streak test identifies a mineral by the color of its powder, made by rubbing it across unglazed
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Luster: The Vocabulary Mineralogists Use for “Shiny”
Quick answer: Luster describes how a mineral’s surface reflects light. The main terms are metallic (pyrite, galena), vitreous or glassy
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Cleavage vs. Fracture: Why Some Minerals Break Clean and Others Don’t
Quick answer: Cleavage is a mineral’s tendency to split along flat planes where its atomic bonds are weakest, producing smooth,
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The Seven Crystal Systems: The Geometry Behind Every Crystal
Quick answer: Every crystal belongs to one of seven crystal systems defined by the symmetry of its atomic structure: cubic
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Staurolite: The Mineral Behind the “Fairy Cross” Twin
Quick answer: Staurolite is an iron-aluminum silicate that often forms twin crystals crossing at 90 or 60 degrees, called “fairy
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Magnetite: The Mineral That Is Actually Magnetic
Quick answer: Magnetite (Fe3O4) is the most magnetic naturally occurring mineral: a magnet sticks to it, and some pieces, called
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Moonstone and Labradorite: The Physics Behind the Glow
Quick answer: Moonstone and labradorite are feldspars whose glow comes from internal structure, not pigment. Moonstone’s floating blue-white sheen (adularescence)
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Obsidian: Volcanic Glass With No Crystal Structure At All
Quick answer: Obsidian is natural volcanic glass: silica-rich lava that cooled so quickly its atoms had no time to arrange
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Crystal Twinning: When Two Crystals Grow as One
Quick answer: Crystal twinning is when two or more crystals of the same mineral grow together in a specific, symmetrical