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Chalcedony

Mineral formula: SiO2

Mineral group: a cryptocrystalline variety of quartz (ie, the crystals are microscopic). Varieties of chalcedony include agate, bloodstone, carnelian, chert, chrysoprase, flint, jasper, onyx, sardonyx, and (most) petrified wood.

Crystal system: trigonal

Crystal habit: fibrous aggregates of parallelly grown ("fibrous") quartz crystals of microscopic and sub-microscopic size. In larger specimens, the "fibers" grow in botryoidal, rounded and stalactitic habits. They often show concentric banding perpendicular to the fiber orientation and are then called Agate.

Cleavage: none

Fracture: conchoidal, sub-conchoidal

Color: colorless, white, to any shade of any color depending on included minerals

Luster: waxy, dull; can be vitreous when polished

Diaphaneity: translucent

Moh’s scale hardness: 6 ½ - 7

Streak: colorless

Specific gravity: 2.6

Named after: the town of Chalcedon, now called Kadıköy, and a district within the city of Istanbul, Turkey.

Geological occurrence: Chalcedony occurs in many different geological settings, including: nodules, vein fillings, crusts in volcanic rocks; as sinter-like crusts in low- to medium temperature hydrothermal veins; in silica-rich marine sedimentary rocks; as nodular concretions and layers in limestones and marls; as a metasomatic replacement in limestones and marls ("replacement chert"); as cement in sandstones; replacing other minerals as pseudomorphs; as a fossilizing material (petrified wood, coral agate).

Energetic properties: Chalcedony has a nurturing energy, promoting feelings of brotherhood, benevolence, generosity, responsiveness, receptivity and good will.

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