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Abstract
Gordaite is a mineral composed primarily of hydrous zinc sodium. Named from its origin of discovery in the Sierra Gorda district of Chile, the gordaite mineral exhibits distinct characteristics of tabular crystals. Despite the inability to completely analyze the chemical composition of the mineral, gordaite is a diverse mineral with a complex aggregate of zinc and sodium composites.

Introduction
Gordaite or Hydrous zinc sodium-rich hydroxyl-chlorosulfate first appeared after a research dive in September of 1984 from the Juan de Fuca Ridge of the northeastern side of the Pacific Ocean. Gordaite was found on weathered deposits as a result of copper smelting in Hettstedt, Germany. The mineral exhibits a hexagonal shape with clear or white (green if cuprian – Cu2+) crystals ranging from planar to broad habit and has a point group of 3. Gordaite findings commonly occur nearby minerals such as sphalerite, bolerite and gypsum. The most recent finding occurred in San Francisco, where copper-zinc sulfide deposits were found. Gordaite’s composition is very similar to the unidentified sample (lCDD)-PDF 41-1421 consisting of the synthetic compound: Zn12(OH)l5(SO4)3Cl3(H2O)5.

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 weighing 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 and sphalerite and were present in the core of the mineral. The sulfate (ZnS) portions were found in concentric layers on the outside of the sample, alternating between [Zn4(OH)6(SO4)Cl]- and [Na(H2O)6]- interlayers

Table 1: Chemical Composition of the Gordaite Mineral (2) NaZn4(SO4)(OH)6CI-6H20.
 * (1) San Francisco mine, Chile; by electron microprobe, H20 by CHN analyzer; low analytical total due to loss of H20 during grinding, Na too high due to peak overlaps with Zn; after adjusting Na20 to 5.5% from AA, and partitioning H between H20 and (OH)l- according to crystal-structure analysis, corresponds to Na1.54Zn3.39(S04)1.0o(OH)6Clo.95 -6H20.

Table 1 is taken from a study done based of the findings in the San Francisco mine. The results indicate that gordaite is primarily composed of a zinc oxide compound with its next highest compounds being ones containing sulfur and water. Section 1 displays the results based from an electron microprobe test which resulted in loss of water. Section 2 displays the normal results taken from crystal structure analysis. Recognition of gordaite crystals is problematic due to its association with tabular barite. 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 barite crystals confirms the idea that gordaite must be more than a byproduct of weathering.

Structure
The gordaite mineral from Juan de Fuca has a hexagonal crystal structure and its formula is Zn4Na1+ (OH)1-6 (SO4)Cl1-∙ 6H1+2O2-. Utilizing electron microprobe 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), the analysis of sodium could not be completed because the layers of zinc (Zn-Lα) were so intense that they prevented researchers from visualizing the Na-K lines. The sample from Germany is a trigonal structure with lattice perimeters: a = 8.364 A° and c = 13.046 Angstroms respectively. Gordaite contains octahedra with edges that share CDI2 – like sheets and have Zn2 ions in their centers, where five hydroxide ions coordinate the Zn2 ions. Throughout the O6 atoms sulfate groups are connected to octahedra sheets. Sodium ions lie between the layers in order to make up for the negative charges and are coordinated by six water molecules.

Physical Properties
Gordaite belongs to the point group P3- (bar over 3). This indicates that the mineral has a primitive lattice and belongs to the hexagonal/trigonal point group. Gordaite structure contains sheets composed of [Zn6(OH)12O2]4- that form edges shared by Zn(OH)6 octahedra. Gordaite crystals are typically white or opaque and can sometimes exhibit a greenish color if cuprian (Cu2+) is present. The crystals are broad and flat and have a vitreous luster. The mineral has a cleavage of {0001}, is flexible and has a hardness of about 2.5. Gordaite measured density is about 2.627 whereas its calculated density is about 2.640. Its axes are a = 8.3556 and c = 13.025, similar to that is the sample from Germany.

Geologic Occurrences
Gordaite has appeared in oxidized deposits of Cu-Zn sulfide in the mines of San Francisco and 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 fluids due to the exterior oxidized portions of the chimney.

Special Characteristics
Although gordaite is a fairly new discovered mineral with few sightings, its formation and intricate layering structure makes for interesting research. The ability of gordaite to discharge hydrothermal fluids with sea water is an important factor of its chemical composition and structure.

Where in the World
The Gordaite mineral was named after the Sierra Gorda District of the Tocopilla Province of the Antofagasta region of Chile. It was approved by the International Mineral Association in 1996. Gordaite has since then been discovered in the San Francisco mines as well as the mine dumps in Germany.

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