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Roger Weller, geology instructor

Aragonite and Calcite
by Christopher Richards
Physical Geology
Spring 2017Fall 2015

                         Calcite vs. Aragonite-The Calcium Carbonate Twins

     A common mineral found everywhere; Calcite has a chemical formula of CaCO3 (Calcium Carbonate).  Calcite and Aragonite both share this chemical formula but have a different crystal structure.  The term for these types of minerals is polymorphs.  Calcite forms trigonal crystals whereas Aragonite forms orthorhombic crystals.  Calcite is the principal constituent of limestone and marble.  It makes up a large portion of the earth’s crust.  It is also serves as a large repository for Carbon and Carbon Dioxide.  Calcite has a hardness of 3 on the Moh’s scale.  Its luster is vitreous, resinous, waxy, or pearly.  Calcite comes in a variety of forms and colors.  It can be found in white, yellow, red, orange, blue, green, brown, and gray.  Calcite effervesces vigorously with hydrochloric acid.    





Lore of Calcite

Calcite is said to increase and amplify energy.  It is associated with decreasing fear and reducing stress.  It promotes creativity and can bring inner peace.  It ignites the imagination and aids in memory.  Those with learning abilities have been known to benefit from Calcite.  The mineral is also used to relieve back pain.  It is known as a stone of reconciliation in relationships.  The astrological sign for Calcite is Cancer.


Devil’s Chimney




Calcite’s Importance

Many of earth’s organisms could not exist without Calcite and Aragonite.  Most invertebrates use these minerals to construct their shells and hard parts.  Good examples are the colorful seashells we find on beaches around the world.  Calcite is mixed with sand to make mortar.  It has been a vital component in construction for many years.  Limestone is composed largely of the mineral Calcite.  Limestone was used to build the pyramids of Egypt and Latin America.  Calcite neutralizes acid in the chemical industry.  High purity Calcite is used to make antacid tablets to fight off heartburn.  Monuments and sculptures of marble are formed from calcite.  The agriculture industry uses Calcite for treating soil. 


The Great Pyramid of Giza is made entirely of Limestone






A naturally occurring carbonate material; Aragonite is a crystal form of Calcium Carbonate (CaCO3).  It forms in oceans, caves, and hot springs.  It can also been found in almost all mollusk shells.  Aragonite has an orthorhombic crystal system with slender, needle-like crystals and is very fragile.  It is the main component of pearl and coral.  It has a hardness of 3.5 to 4 on Moh’s scale.  Aragonite may contain sand inclusions which gives it a brown color.  Other colors include white, gray, yellow, red, pink, purple, orange, blue, and green.  Aragonite clusters from Morocco are peachy brown. Its luster is vitreous to dull.  The crystals are transparent to opaque.  Aragonite has a famous crystal habit called twinning.  It is a growth error where the crystals form twinned pseudo-hexagonal prismatic shapes.  Aragonite is unstable at standard temperatures and converts to Calcite over time.     


Aragonite from Morocco



Lore of Aragonite

Aragonite was discovered in 1797 in Aragon province, Spain.  It can also be found in Mexico, New Mexico, Arizona, and the seabed of the Bahama Islands.  Fine Aragonite crystals can be found in Bisbee, AZ.  Gorgeous crystals of Aragonite have been found in Wind Cave, South Dakota.  Aragonite may be found as porous rock in Turkey.  Aragonite is said to be a good earth healer.  The stone itself is a stabilizer and raises energy vibes.  It has been known to relieve stress and nerve problems.  Aragonite has also been used to treat depression and is said to bring peace and tranquility.  Its astrological sign is Capricorn.  Natural pearls are almost entirely formed by aragonite, which bonds with conchiolin.  Some believe Aragonite has the power to overcome false illusions and bring out the truth.  In the 15th century, Aragonite was carved for masks.  In 1876, it became very popular in Europe due to its translucency.  It was sold at extravagant prices.



Blue Aragonite – The Peace Stone


Image result for aragonite jewelry



Aragonite’s Importance

Aragonite is essential for replication of reef conditions.  It provides materials to maintain sea life and keeps PH of water close to its natural level.  It helps remove pollutants like zinc, cobalt, and lead from water.  Aragonite is a minor constituent of limestone.  It is used in steel production and other structures made of cement.  Due to its beautiful colors, it is a popular gemstone.  It used to make jewelry and a heart-shaped Aragonite gem is adored.  Aragonite is also used to make glass and helps condition the soil.  The natives of Pueblo still carve crucifixes, stone fruit, and paperweights from Aragonite.  Pakistan onyx and alabaster are made of Aragonite.


Aragonite sand beach (Fernandez Bay, San Salvador Island, Bahamas)

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Many of the whitish-colored lime sand beaches in the world are composed of Aragonite sediments.  Some shallow, warm ocean environments contain milky seawater.  This milky seawater contains tiny hair-like needles of Aragonite.