Sodalite
Authors: Chona, Will, and Rogelio
Mineral Name: Sodalite
Chemical Composition: Na8[Al6Si6O24]Cl2 (#1)
Color: Most commonly bluish to greyish; however, it has been found in yellowish and light black as well. (#1) It can be seen in rare colors of purple, pink, green, brown, white and colorless. (#2)
Streak: White, bluish (#2) (#13)
Hardness: 5.5-6.0 (#1)
Cleavage/Fracture: Sodalite has poor cleavage in six directions that is hardly noticeable and it has uneven fracture with a rough or irregular surface. (#2)
Crystal Form: The crystal form appears, very rarely, as dodecahedral (12 sided polyhedron). (#2) Sodalite has an aggregate form of being grainy (similar to an array of grains), massive (has no definite shape or form) and nodular (a shape of a small rounded lump). (#2)
Luster: Vitreous to greasy, (#1) (#2)
Special Features: Sodalite has a rare mineral phenomenon called photochromism. Sodalite when placed in the dark will glow brighter with its existing colors or will even show colors that aren't present like yellow. Another feature of sodalite is its fluorescence which means that it produces its own light. This allows the rock to glow in the dark under ultraviolet light. This is only seen in certain types of sodalite. (#5)
Varieties: Hackmanite is a sulfur-rich variety of sodalite. It is usually pink or purple in color. (#2) Germanate sodalite is an artificial sodalite variety. The chemical formula of this mineral contains germanium instead of silicon. (#7) Molybdosodalite contains molybdenum oxide and it has pale green crystals that occurs with humite, vesuvianite and garnet in ejected limestone blocks of Monte Somma, a part of the Somma-Vesuvius volcanic complex. (# 6, 8)
Mineral Group: Sodalite belongs to the silicate, tectosilicate, and feldspathoid groups. (#2) Silicate minerals contain the elements of silicon and oxygen. (#14) Tectosilicates are a group of silicate minerals that have four oxygen atoms from each tetrahedron shared with other silica tetrahedrons.(#15) Feldspathoid minerals are primarily comprised of silicate minerals; however, feldspathoids crystallize from silica-deficient melts. (#1)
Environment: Sodalite can form and occur in alkaline intrusive and extrusive igneous environments. It forms from silica-deficient melts. (#1) It is not limited to one specific region of the Earth and has been found on several other continents but most notably Greenland. It is also found in skarns. Skarns are metamorphic rock that is altered by a process called metasomatism. Metasomatism occurs when hot, chemically active fluids flow through a rock and cause recrystallization of minerals and a change in composition. (#20) Mostly skarns form from the alteration of limestone, dolostone and marble. (#20)
Associated Rock types: Sodalite is mainly found in igneous rocks. Intrusive rocks that contain sodalite are sodalitolite but also sodalite-bearing syenite, diorite, and gabbro.(#16) Extrusive rocks that contain sodalite are sodalitite as well as sodalite-bearing phonolite.(#11,16) Sodalite is also found in metamorphic skarns.(#2)
Occurrence in North America: Sodalite can be found in Dennis Hill in Litchfield, Maine; Magnet Cove, Arkansas; Dungannon Township in Ontario, Canada; Mont Saint Hilaire, Quebec;
Kicking Horse Pass and Ice River in Golden Mining Division, British Columbia; and in Ilimaussaq Alkaline Complex in Greenland. (#2)
Economic Uses: Sodalite is a very versatile and useful mineral. The use of sodalite spans from inexpensive jewelry. (#13) Earrings, pins and pendants are the most common jewelry produced with sodalite. It may also be used in small sculptures as well. Sodalite is not suitable for making rings or bracelets because of its hardness and these types of jewelry are prone to scratches. Although sodalite is considered “rare”, it is one of the only vividly blue minerals worthy of gem material. However, there is no market/demand for this beautifully deep blue mineral, therefore jewelry stores do not stock it often. (#13) Also because it is difficult to produce a standard product appearance, it is nearly impossible to create a line of product worthy of big box stores. (#13)
Industrial Uses: There has been a significant increase in interest of sodalite and other closely related minerals to create industrial chemicals. To produce quality chemicals, people have traditionally used a method called Hydrothermal Synthesis (#9). This method is basically heating sodalite (and other minerals) through water to a very high temperature within a reactor. This environment places certain combinations of materials under pressure to produce a desired industrial chemical. The disadvantage to this process is the discarded and polluted waste water it creates as well as the lack of energy efficiency used in heating the water. (#9)
However, when sodalite is heated with microwaves and hydrothermal methods, it yields the same results as above but creates a chain reaction of increased efficiency. This means less water waste created and less energy used. This eco-friendly and “cost-effective” method to produce chemicals and another economic mineral, zeolites, is the future in terms of large scale production of industrial chemicals. (#9)
First Notable Identification: Sodalite was first discovered in 1811 in Greenland where the mineral was analyzed and named by Thomas Thomson, a Scottish chemist (#’s 3, 5). He wrote about his findings in an article titled “ A Chemical Analysis of Sodalite, A New Mineral in Greenland”. He described,“Sodalite occurs in a primitive rock mixed with sahlite, augite, hornblende and garnet. It occurs massive and crystallised in rhomboidal dodecahedrons. Its colour is intermediate between celandine and mountain green. No mineral has hitherto been found containing nearly so much soda as this. Hence the reason of the name by which I have distinguished it.”(# 4)
How We Identified It: The vivid blue color makes this mineral standout in comparison to several other minerals which have traditionally more subtle and earthy tones. We also identified this mineral with its white veins or lines (calcite) that are distinct.
Don’t Confuse It With: Sodalite can be confused with lazurite. A sure way to tell them apart is that lazurite has a blue streak and sodalite has a white streak. However, both of these minerals can have a similar color and both minerals can have white veining that makes it hard to tell one apart from the other. This makes sodalite a perfect alternative to people who enjoy lapis lazuli but don't want to shovel money into it. (#18)
Sodalite can also be mistaken for lazulite which is another blue mineral, but lazulite does not have any white veins and is not fluorescent, unlike sodalite . (#17)
Azurite is another blue mineral that can be confused with sodalite. The biggest differences between these two minerals is that azurite is softer and will have a blue streak instead of sodalite’s white streak. (#19)
Bibliography:
#1 Allaby, M. (2013). Sodalite. A Dictionary of Geology and Earth Sciences, A Dictionary of Geology and Earth Sciences.
#2 “Sodalite: The Mineral Sodalite (Hackmanite) Information and Pictures.” Sodalite: The Mineral Sodalite (Hackmanite) Information and Pictures, www.minerals.net/mineral/sodalite.aspx.
#3 “Sodalite.” Sodalite Gemstone Information, www.gemdat.org/gem-3701.html.
#4 Thomson, Thomas. “A Chemical Analysis of Sodalite, a New Mineral from Greenland.” The Medical and Physical Journal, Printed for R. Phillips, Oct. 1811, www.ncbi.nlm.nih.gov/pmc/articles/PMC5699400/?page=1.
#5 Admin. “Properties and Virtues of Sodalite.” Kabeer Agate Blog Site, 8 Mar. 2019, www.kabeeragate.com/blog/properties-and-virtues-of-sodaliteu/.
#6 “Molybdosodalite.” Molybdosodalite: Mineral Information, Data and Localities., www.mindat.org/min-27360.html.
#7 “Germanate-Sodalite.” Germanate-Sodalite: Mineral Information, Data and Localities., www.mindat.org/min-9394.html.
#8 Minerals of Vesuvius, www.minsocam.org/msa/collectors_corner/arc/vesuviusii.htm.
#9 Zeng, Shangjing, et al. “Solventless Green Synthesis of Sodalite Zeolite Using Diatomite as Silica Source by a Microwave Heating Technique.” Inorganic Chemistry Communications, vol. 70, 2016, pp. 168–171.
#10 “Nepheline-Syenite.” Nepheline-Syenite: Mineral Information, Data and Localities., www.mindat.org/min-48350.html.
#11 “Phonolite.” Phonolite: Mineral Information, Data and Localities., www.mindat.org/min-48540.html.
#12 “Trachyte.” Trachyte: Mineral Information, Data and Localities., www.mindat.org/min-48478.html.
#13 Hobart M. King, Ph.D., RPG https://geology.com/minerals/sodalite.shtml
#14 “Silicates - Minerals.net Glossary of Terms.” Silicates - Minerals.net Glossary of Terms, www.minerals.net/mineral_glossary/silicates.aspx.
#15 “Tectosilicates - Minerals.net Glossary of Terms.” Tectosilicates - Minerals.net Glossary of Terms, www.minerals.net/mineral_glossary/tectosilicates.aspx.
#16 “Sodalite.” Sodalite: Mineral Information, Data and Localities., www.mindat.org/min-3701.html.
#17 “Lazulite: The Blue Mineral Lazulite: Information and Pictures.”Lazulite: The Blue Mineral Lazulite: Information and Pictures,
www.minerals.net/mineral/lazulite.aspx.
#18 “Lazurite: The Blue Mineral Lazurite: Lapis Information and Pictures.” Lazurite: The Blue Mineral Lazurite: Lapis Information and Pictures, www.minerals.net/mineral/lazurite.aspx.
#19 “Azurite: The Blue Mineral Azurite Information and Pictures.” Azurite: The Blue Mineral Azurite Information and Pictures, www.minerals.net/mineral/azurite.aspx.
#20 King, Hobart M. “Skarn.” Geology, geology.com/rocks/skarn.shtml.