Hilgardite is a

borate mineral The borate minerals are minerals which contain a borate anion group. The borate (BO3) units may be polymerised similar to the SiO4 unit of the silicate mineral class. This results in B2O5, B3O6, B2O4 anions as well as more complex structures whic ...

with the chemical formula Ca₂B₅O₉Cl·H₂O. It is

transparent Transparency, transparence or transparent most often refer to: * Transparency (optics), the physical property of allowing the transmission of light through a material They may also refer to: Literal uses * Transparency (photography), a still, ...

and has

vitreous Vitreous may refer to: Materials * Glass, an amorphous solid material ** Vitreous enamel, a material made by fusing powdered glass to a substrate by firing * Vitreous lustre, a glassy luster or sheen on a mineral surface Biology * Vitreous body, ...

luster. It is colorless to light pink with a white streak. It is rated 5 on the

Mohs Scale The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by th ...

. It crystallizes in the

triclinic 180px, Triclinic (a ≠ b ≠ c and α ≠ β ≠ γ ) In crystallography, the triclinic (or anorthic) crystal system is one of the 7 crystal systems. A crystal system is described by three basis vectors. In the triclinic system, the crystal is ...

crystal system. Crystals occur as distorted tabular triangles and are hemimorphic,

polytypes In materials science, polymorphism describes the existence of a solid material in more than one form or crystal structure. Polymorphism is a form of isomerism. Any crystalline material can exhibit the phenomenon. Allotropy refers to polymorphism ...

exist.Handbook of Mineralogy
/ref> It was named for geologist

Eugene W. Hilgard Eugene Woldemar Hilgard (January 5, 1833, Zweibrücken, Rhineland-Palatinate, Germany – January 8, 1916, Berkeley, California, United States) was a German-American expert on pedology (the study of soil resources). An authority on climate as a pe ...

(1833–1916). It was first described in 1937 for an occurrence in the Choctaw Salt Dome of

Iberville Parish Iberville Parish (french: Paroisse d'Iberville) is a List of parishes in Louisiana, parish located south of Baton Rouge in the U.S. state of Louisiana, formed in 1807. The parish seat is Plaquemine, Louisiana, Plaquemine. At the 2010 U.S. census, ...

Louisiana Louisiana , group=pronunciation (French: ''La Louisiane'') is a state in the Deep South and South Central regions of the United States. It is the 20th-smallest by area and the 25th most populous of the 50 U.S. states. Louisiana is borde ...

, US.Mindat.org
/ref> It occurs as an uncommon accessory mineral in

evaporite An evaporite () is a water-soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as ocea ...

deposits and

salt dome A salt dome is a type of structural dome formed when salt (or other evaporite minerals) intrudes into overlying rocks in a process known as diapirism. Salt domes can have unique surface and subsurface structures, and they can be discovered using ...

s worldwide. In addition to the type locality it has been reported in

Wayne County, Mississippi Wayne County is a county located in the U.S. state of Mississippi. As of the 2010 census, the population was 20,747. Its county seat is Waynesboro. The county is named for General Anthony Wayne. Geography According to the U.S. Census Bureau, ...

and in the

Louann Salt The Louann Salt is a widespread evaporite formation that formed in the Gulf of Mexico during the Callovian in the mid Jurassic. The Louann formed in a rift as the South American and North American Plates separated, from an embayment of the Pacific ...

Formation,

Clarke County, Alabama Clarke County is a county located in the southwestern part of the U.S. state of Alabama. As of the 2020 census, the population was 23,087. The county seat is Grove Hill. The county's largest city is Jackson. The county was created by the leg ...

in the United States and at the Penobsquis and Salt Springs evaporites, near Sussex, New Brunswick, Canada. In Europe it is reported from the Konigshall-Hindenburg

potash Potash () includes various mined and manufactured salts that contain potassium in water-soluble form.

mine near

Göttingen Göttingen (, , ; nds, Chöttingen) is a college town, university city in Lower Saxony, central Germany, the Capital (political), capital of Göttingen (district), the eponymous district. The River Leine runs through it. At the end of 2019, t ...

Lower Saxony Lower Saxony (german: Niedersachsen ; nds, Neddersassen; stq, Läichsaksen) is a German state (') in northwestern Germany. It is the second-largest state by land area, with , and fourth-largest in population (8 million in 2021) among the 16 ...

, Germany and in the Boulby potash mine,

Whitby Whitby is a seaside town, port and civil parish in the Scarborough borough of North Yorkshire, England. Situated on the east coast of Yorkshire at the mouth of the River Esk, Whitby has a maritime, mineral and tourist heritage. Its East Clif ...

Yorkshire Yorkshire ( ; abbreviated Yorks), formally known as the County of York, is a Historic counties of England, historic county in northern England and by far the largest in the United Kingdom. Because of its large area in comparison with other Eng ...

, England. In Asia it is reported from the Chelkar salt dome, Uralsk district,

Kazakhstan Kazakhstan, officially the Republic of Kazakhstan, is a transcontinental country located mainly in Central Asia and partly in Eastern Europe. It borders Russia to the north and west, China to the east, Kyrgyzstan to the southeast, Uzbeki ...

; the Ilga Basin, eastern

Siberia Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part of ...

, Russia and the Sedom Formation,

Mount Sedom Mount Sodom ( he, הר סדום, ''Har Sedom'') is a hill along the southwestern part of the Dead Sea in Israel; it is part of the Judaean Desert Nature Reserve. It takes its name from the legendary city of Sodom, whose destruction is the subje ...

Dead Sea The Dead Sea ( he, יַם הַמֶּלַח, ''Yam hamMelaḥ''; ar, اَلْبَحْرُ الْمَيْتُ, ''Āl-Baḥrū l-Maytū''), also known by other names, is a salt lake bordered by Jordan to the east and Israel and the West Bank ...

Israel Israel (; he, יִשְׂרָאֵל, ; ar, إِسْرَائِيل, ), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a country in Western Asia. It is situated ...

References

* S. Ghose and C. Wan, ''Hilgardite, Ca₂ ₅O₉l·H₂O; a piezoelectric zeolite-type pentaborate'', American Mineralogist; February 1979; v. 64; no. 1-2; p. 187-195 * Burns, P. C. and F. C. Hawthorne, ''Refinement of the structure of Hilgardite-1A'', Acta crystallographica. Section C, 1994, vol. 50 (5), pp. 653–655 {{Commons category Calcium minerals Tektoborates Halide minerals Triclinic minerals Evaporite Borate chlorides Minerals in space group 1

See also

References