Gordaite is a

sulfate mineral The sulfate minerals are a class of minerals that include the sulfate ion () within their structure. The sulfate minerals occur commonly in primary evaporite depositional environments, as gangue minerals in hydrothermal Vein (geology), veins and as ...

composed primarily of

hydrous In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...

chloride The term chloride refers to a compound or molecule that contains either a chlorine anion (), which is a negatively charged chlorine atom, or a non-charged chlorine atom covalently bonded to the rest of the molecule by a single bond (). The pr ...

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It ...

with formula: NaZn₄(SO₄)(OH)₆Cl·6H₂O. It was named for the discovery location in the

Sierra Gorda The Sierra Gorda () is an Ecoregion, ecological region centered on the northern third of the List of states of Mexico, Mexican state of Querétaro and extending into the neighboring states of Guanajuato, Hidalgo (state), Hidalgo and San Luis Po ...

district of

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

. Gordaite forms as tabular

trigonal In crystallography, the hexagonal crystal family is one of the six crystal family, crystal families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While commonly confused, the tr ...

crystals. Gordaite first appeared after a research dive in September 1984 from the

Juan de Fuca Ridge The Juan de Fuca Ridge is a Mid-ocean ridge, mid-ocean spreading center and divergent plate boundary located off the coast of the Pacific Northwest region of North America, named after Juan de Fuca. The ridge separates the Pacific Plate to the we ...

of the northeastern side of the Pacific Ocean. Gordaite was also described from weathered

slag The general term slag may be a by-product or co-product of smelting (pyrometallurgical) ores and recycled metals depending on the type of material being produced. Slag is mainly a mixture of metal oxides and silicon dioxide. Broadly, it can be c ...

deposits as a result of

copper smelting Smelting is a process of applying heat and a chemical reducing agent to an ore to extract a desired base metal product. It is a form of extractive metallurgy that is used to obtain many metals such as iron, copper, silver, tin, lead and zinc. Sm ...

Hettstedt Hettstedt () is a town in Mansfeld-Südharz district, Saxony-Anhalt, Germany, on the Wipper. It consists of Hettstedt proper and the ''Ortschaften'' (municipal divisions) Ritterode and Walbeck.n4Na(OH)6(SO4)Cl•6H2O second occurrence in the Juan de Fuca Ridge, and new data. American Mineralogist 83, pg. 1111-1116. The mineral exhibits a

hexagonal In geometry, a hexagon (from Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°. Regular hexagon A regular hexagon is d ...

shape with clear or white (green if cuprian – Cu²⁺) crystals ranging from planar to broad habit and has a

point group In geometry, a point group is a group (mathematics), mathematical group of symmetry operations (isometry, isometries in a Euclidean space) that have a Fixed point (mathematics), fixed point in common. The Origin (mathematics), coordinate origin o ...

of . Gordaite commonly occurs near minerals such as

sphalerite Sphalerite is a sulfide mineral with the chemical formula . It is the most important ore of zinc. Sphalerite is found in a variety of deposit types, but it is primarily in Sedimentary exhalative deposits, sedimentary exhalative, Carbonate-hoste ...

boleite Boleite is a complex halide mineral with formula: KPb26Ag9Cu24(OH)48Cl62. It was first described in 1891 as an oxychloride mineral. It is an isometric mineral which forms in deep-blue cubes. There are numerous minerals related to boleite, such ...

and

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate Hydrate, dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk ...

. The most recent finding occurred in the San Francisco mine in Chile where copper-zinc sulfide deposits were found.

Composition

The 1998 Nasdala article examines the ALV 1457-5R sample found on the sea floor of the Juan de Fuca Ridge. The sample itself was taken from a sulfide chimney with mass of about 2.5 kg. The chimney was composed of about 98% permeable sulfides and 2% sulfates. The sulfides were primarily composed of iron sulfides such as

pyrite The mineral pyrite ( ), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic luster and pale brass-yellow hue ...

and

and were present in the core of the chimney. The sulfate portions were found in concentric layers on the outside of the sample, alternating between n₄(OH)₆(SO₄)Cl and a(H₂O)₆ interlayers. ''Table 1: Chemical Composition of the Gordaite Mineral'' **(1) San Francisco mine, Chile; by electron microprobe, H₂O by CHN analyzer; low analytical total due to loss of H₂O during grinding, Na too high due to peak overlaps with Zn; after adjusting Na₂O to 5.5% from AA, and partitioning H between H₂O and (OH)- according to crystal-structure analysis, corresponds to Na_1.54Zn_3.39(S0₄)(OH)₆Cl_0.95·6H₂0. **(2) NaZn₄(SO₄)(OH)₆Cl·6H₂0.Downs R T (2006) The RRUFF Project: an integrated study of the chemistry, crystallography, Raman and infrared spectroscopy of minerals. Program and Abstracts of the 19th General Meeting of the International Mineralogical Association in Kobe, Japan. O03-13 Table 1 is taken from a study done based on the findings in the San Francisco mine. Section 1 displays the results based from an electron microprobe test which resulted in loss of water. Section 2 displays the normalized results taken from crystal structure analysis. Recognition of gordaite crystals is problematic due to its association with tabular

baryte Baryte, barite or barytes ( or ) is a mineral consisting of barium sulfate (Ba S O4). Baryte is generally white or colorless, and is the main source of the element barium. The ''baryte group'' consists of baryte, celestine (strontium sulfate), ...

. Based on the findings of the dive at Juan de Fuca Ridge, gordaite was formed due to the ''reaction of discharging hydrothermal fluids with sea water''. The overwhelming presence of baryte crystals confirms the idea that gordaite must be more than a byproduct of

weathering Weathering is the deterioration of rocks, soils and minerals (as well as wood and artificial materials) through contact with water, atmospheric gases, sunlight, and biological organisms. It occurs '' in situ'' (on-site, with little or no move ...

Structure

The gordaite mineral from Juan de Fuca has a trigonal crystal structure and its formula is Zn₄Na(OH)₆(SO₄)Cl·6H₂O. Utilizing

electron microprobe An electron microprobe (EMP), also known as an electron probe microanalyzer (EPMA) or electron micro probe analyzer (EMPA), is an analytical tool used to non-destructively determine the chemical composition of small volumes of solid materials. I ...

analysis to define gordaite’s chemical composition is difficult because of its intricate chemical layering. According to the study done using the Philips XL 30 SEM (

scanning electron microscope A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that ...

), the analysis of sodium could not be completed because the lines of zinc (Zn-Lα) were so intense that they overlapped the Na-K lines. The sample from Germany is a trigonal structure with lattice perimeters: a = 8.364 Å and c = 13.046 Å respectively. Gordaite contains octahedra with edges that share CDI2 – like sheets and have Zn²⁺ ions in their centers, where five hydroxide ions coordinate the zinc ions. Throughout the sulfate groups are connected to octahedral sheets. Sodium ions lie between the layers in order to make up for the negative charges and are coordinated by six water molecules.Adiwidjaja G., Friese K., Klaska K.-H. and Schluter J. (1997): ''The crystal structure of gordaite NaZn4(SO4)(OH)6Cl·6H2O,'' Zeitschrift für Kristallographie, 212, 704–707

Physical properties

Gordaite belongs to the point group P. This indicates that the mineral has a primitive lattice and belongs to the hexagonal/trigonal point group. Gordaite crystals are typically white or opaque and can sometimes exhibit a greenish color if trace copper is present. The crystals are broad and flat and have a vitreous luster. The mineral shows a cleavage plain parallel to , is flexible and has a Mohs hardness of about 2.5. The measured

specific gravity Relative density, also called specific gravity, is a dimensionless quantity defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for solids and liquids is nea ...

is about 2.627 whereas the calculated value is about 2.640. Its crystallographic axes are a = 8.3556 and c = 13.025

angstrom The angstrom (; ) is a unit of length equal to m; that is, one ten-billionth of a metre, a hundred-millionth of a centimetre, 0.1 nanometre, or 100 picometres. The unit is named after the Swedish physicist Anders Jonas Ångström (1814–18 ...

s, similar to that is the sample from Germany.Schlüter, J., Klaska, K.-H., Friese, K., Adiwidjaja, G. and Gebhard, G. (1997): Gordaite, NaZn4(SO4)(OH)6Cl•6H2O, a new mineral from the San Francisco Mine, Antofagasta, Chile. Neues Jahrbuch für Mineralogie, Monatshefte (1997): 155-162.

Geologic occurrences

Gordaite has appeared in oxidized deposits of Cu-Zn sulfide in the mines of San Francisco, Chile. Deposits have also been found on the eroded mine dumps in Hettstedt and Helbra Germany. The most notable incidence occurred on the sea floor of the Juan de Fuca Ridge. This occurrence is important because it shows the reaction of ocean water with

hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

fluids in the exterior oxidized portions of the chimney. Gordaite was named after the

District of the

Tocopilla Province Tocopilla Province () is one of the three provinces in the northern Chilean region of Antofagasta (II). Its capital is the city of Tocopilla. Geography and demography According to the 2012 census by the National Statistics Institute (''INE''), t ...

of the

Antofagasta Antofagasta () is a port city in northern Chile, about north of Santiago. It is the capital of Antofagasta Province and Antofagasta Region. According to the 2015 census, the city has a population of 402,669. Once claimed by Bolivia follo ...

region of Chile where it has been reported from the San Francisco mines and other locations. It was approved by the

International Mineralogical Association Founded in 1958, the International Mineralogical Association (IMA) is an international group of 40 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 5000 plus known mineral species. ...

in 1996. Gordaite has since been reported from mine dumps in Germany and the Juan de Fuca Ridge.

References

{{reflist Zinc minerals Sodium minerals Sulfate minerals Trigonal minerals Minerals in space group 147 Minerals described in 1997