Aragonite Vs. Chalcedony

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Quick Facts on Differences of Aragonite and Chalcedony

• While both aragonite and chalcedony can be hexagonal, in terms of crystallography, aragonite can be orthorhombic and chalcedony can be trigonal.
• For chemical formulas, aragonite is CaCO3 while chalcedony is SiO2.
• While both aragonite and chalcedony can be dull or vitreous, in terms of luster, aragonite can be resinous and chalcedony can be waxy.
• Aragonite can be commonly green while chalcedony can be commonly red.
• Aragonite's rarity is more rare than chalcedony.
• Aragonite's hardness is lower than chalcedony - aragonite ranges from 3.5 to 4 and chalcedony is 7 on the Moh's scale.
  • Aragonite can be scratched by the average knife blade (4.5), glass (5.5) or quartz (7) while chalcedony can not be.

  Quick Facts on Similarities of Aragonite and Chalcedony

  • Aragonite and chalcedony both can be opaque, translucent or transparent.
  • Aragonite and chalcedony both streak white.

  Summary of Aragonite

  Aragonite is a mineral that is commonly found in sedimentary rocks such as limestone, dolomite, and marble. It is a polymorph of calcium carbonate, which means that it has the same chemical formula as calcite but a different crystal structure. Aragonite is named after the Aragon region in Spain where it was first discovered.

  Summary of Chalcedony

  Chalcedony is a mineral that is widely used in jewelry making, carvings, and decorative objects. It is a member of the quartz family and is composed of microscopic crystals of quartz that are arranged in a fibrous or microcrystalline structure. The mineral is typically translucent or opaque and can come in a range of colors, including white, gray, blue, brown, and red. Chalcedony is often found in association with other minerals such as agate, jasper, and onyx.

  Table Comparison of Aragonite vs Chalcedony

  Aragonite (src)	Chalcedony (src)
  Transparency	transparent, translucent, opaque	transparent, translucent, opaque
  Chemical Formula	CaCO3	SiO2
  Chemical Composition	calcium carbonate	silicon dioxide
  Specific Gravity	2.93, 2.947, 2.95, 3	2.55, 2.91
  Hardness	3.5, 4	7
  Streak	white	white
  Crystallography	orthorhombic, hexagonal	hexagonal, trigonal
  Refractive Index	1.53, 1.685	1.54, 1.553
  Hydrous	No	No
  Colors	common: green sometimes: red, blue less common: gray, pink, brown, white, orange, purple, yellow, lavender, colorless	common: red sometimes: blue, gray, pink, black, brown, green, white, orange, purple, yellow, band, multicolor
  Category	carbonate	quartz
  Fracture	subconchoidal	conchoidal