Goyazite - Encyclopedia

    Class : Phosphates, arsenates, vanadates
    Subclass : Hydrated phosphates
    Crystal system : Trigonal
    Chemistry : SrAl3(PO4)2(OH)5 H2O
    Rarity : Uncommon

Goyazite (also called hamlinite) is an uncommon phosphate from magmatic and hydrothermal contexts; it is indeed found in granitic pegmatites and greisens, zones of clayey hydrothermal alteration, carbonatites, etc... Resistant, it is also an alluvium mineral. It owes its name to its locality of discovery : Serra de Congonhas in the province of Goyaz (Brazil). Goyazite crystals are rhombohedral, sometimes pseudocubic or tabular, colorless or whitish, straw yellow to yellow-brown, sometimes orange.

Main photo : Goyazite from Binn, Valais, Switzerland © Stephan Wolfsried

2.8 cm goyazite from Fuchsbau quarry, Bavaria, Germany © Karlheinz Gerl
Goyazite from Binn, Valais, Switzerland © Joy Desor
Goyazite from Clara Mine, Germany  © Michael Förch
Goyazite from Bois-de-la-Roche quarry, Loire-Atlantique, France © Pierre Le Roch

Goyazite in the World

The world's finest goyazite crystals are stunning yellow hexagonal tabular specimens up to 3 cm from Fuchsbau (Fichtelgebirge, Germany). The Lengenbach quarry, near Binn in the Swiss Valais, contains good 3 mm hexagonal crystals, embedded in dolomite geodes. Among the many other localities, mention should be made of the crystals of Goldkuppe (Namibia), those of the wolframite veins of Eagle Rock (Colorado), the pegmatites of Maine, and the diamondiferous gravels of the state of Goyaz (Brazil), the type locality.

Goyazite in France

In France, goyazite is known at Echassières (Allier) as well as at the Bois-de-la-Roche quarry (Loire-Atlantique).

Twinning

No twin known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 4.5 to 5
Density : 3.26
Fracture : Undetermined
Streak : White

TP : Translucent to transparent
RI : 1.620 to 1.651
Birefringence : 0.013
Optical character : Uniaxial +
Pleochroism : Low
Fluorescence : None

Solubility : Acids

Magnetism : NoneRadioactivity : None

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