Magura Uroiului type locality (ROMANIA) (photo by F. Forray)

Magura Uroiului type locality (ROMANIA)

by Marcel Benea and Ferenc Forray

Măgura Uroiului Hill represents the type locality for pseudobrookite: (Fe³⁺,Fe²⁺)₂(Ti,Fe²⁺)O₅; the idealised formula is Fe₂TiO₅. The mineral was first time identified and described from this occurrence in 1878 by Professor Antal Koch, from the University in Cluj.

How to get there

County: Hunedoara (Romania)
Locality: Uroi, ~13 Km from Deva
GPS location: Lat N 45.85864 / Long E 23.04077
Trail track: uroi.gpx (by F. Forray). If you don't have a program to read GPX files, download for free the EasyGPS program.
	Map of the region (click for bigger map)

LOCATION: Măgura Uroiului Hill is located 3 km north-east from Simeria, on the right side of Mureş Valley (at an altitude of about 200 m from the river bed), and it spreads on about 1 km². Geologically, the area is located in the southern part of Metalliferous Mountains, on the left slope of Rapolt crystalline island (Fig. 1).

In the old Hungarian and German references, this hill was named Aranyer Berg (“the Golden Hill”) due to the “golden” colour of the hill’s slopes at sunset.

Geology and mineralogy

Măgura Uroiului Hill has a bulge-like shape, with a steep southern slope and a smooth northern one. The terrace-like morphologies in its south-eastern side point to an intense anthropic activity. Thus, Schafarzik (1909) mentioned the opening of a first quarry at Uroi only in 1866, when the construction of the first railway in Transylvania had started. However, other authors (Pascu, 1932; Pîrvu, 1964; Tudor, 1968; Wollmann, 1996) have mentioned several very old stone quarries in the area, documented by the presence of shards of Dacian and Roman ceramics.

Fig. 1. Location of the pseudobrookite occurence (Măgura Uroiului Hill)

From petrographic point of view, the rocks have been subsequently described as andesites with augite (Koch, 1878) showing two varieties (greyish, and respectively reddish), andesites with pseudobrookite (Laţiu, 1937), lava flows and pyroclastic rocks (Berbeleac, 1962), and finally as trachyandesites (Savu et al., 1994) displaying two facies-types: a grey facies, and a reddish (hematitic) one.

Berbeleac (1962) considered that the bulge-type morphology of the hill does not imply the preservation of a single volcanic vent, but that it resulted from the generation of three successive andesitic lava emissions, each showing distinctive structural-textural features, which were accompanied by pyroclastic products (Fig. 2).

The first lava emission, represented by grey andesites covers the base of the hill and it crops out in the small quarries located in the close vecinity of Mureş River or of the Uroi–Rapoltu Mare road. The second lava generation is well-preserved in outcrops; it builds-up the steep slope of the Măgura Uroiului Hill along three of its borders (east, west and south). From mineralogical and petrographical point of view, these rocks resemble the first lava generation, the only difference being its red-crimson colour. The third lava generation is located in the highest part of the hill, being separated from the second generation of lava by a thin level of pyroclastic rocks. As opposite to the previous lava layers, the third one is brown-reddish in colour, the rock is more porous and softer, and the fluidal texture is dominant. The northern part of the hill, where the third lava generation is present is entirely covered by soil and alluvial deposits, only a small patch located east-, south- and south-westwards being visible.

According to Roşu et al. (2004), the andesites with pyroxenes from the Măgura Uroiului Hill represent the youngest (1.6 My) products of the alkaline magmatism in the Apuseni Mountains, having a pronounced shoshonitic character.

One of the typical features of the andesites is represented by the frequent enclaves consisting of gabbros, diorites, and metamorphic rocks fragments, surrounded by reaction coronas containing macroscopically-visible crystals of garnets (andradite), epidote, diopside, and hematite. The silica-rich enclaves consist of SiO₂ polymorphs, especially tridymite. The mineralogical composition of the andesites includes plagioclase feldspars (andesine), monoclinic pyroxenes (augite), rhombic pyroxenes (hypersthene), biotite, apatite, magnetite and hematite.


Fig. 3. Pseudobrookite (black), besides hypersthene (reddish), image width: 0.5 cm	Fig. 4. Pseudobrookite crystal

Pseudobrookite is present only in the reddish andesites (corresponding to the second lava flow), both in the rock matrix and in the fissures, as tabular crystals (Fig. 3, 4), up to 5 mm; it has black colour and a strong metallic lustre and in almost all the cases it forms an assemblage with hypersthene and hematite. Crystallographic and mineralogical studies on pseudobrookite were performed by Koch (1878), von Rath (1880), Traube (1892) and Laţiu (1937). The main mineralogical features are included in Table 1.

Table 1 Pseudobrookite – main mineralogical features (PDF-card 41-1432, ICSD, 1998)

Chemical formula	Fe₂TiO₅ ; (Fe³⁺,Fe²⁺)₂(Ti,Fe²⁺)O₅
Colour	Black, black-brownish, brown-reddish
Streak	brownish
Lustre	metallic
Transparency	opaque
Cleavage	not visible
Fracture	conchoidal
Crystal forms	prismatic to tabular, acicular in radial display
Crystal system	rhombic
Cell parameters	a=9.796; b=9.981; c=3.720; Z=4; V=364.71
Space group	Bbmm
X-ray diffraction (I/I₀)	3.486 (1) 2.752 (1) 4.901 (4)
Mohs hardness	6 – 6.5
Density	4.39
Appearance	as druses- and voids-fillings in volcanic rocks
Occurrences	Romania (Măgura Uroiului), Italy (Vesuvius, Etna)

Hypersthene, present as elongated crystals of small sizes (0.5-1 mm) and red colour has been described by Krenner as a new mineral species ("szaboite"); later on it was proven that is represents an oxidized variety of hypersthene (Udubaşa et al.,1992).

REFERENCES

Berbeleac I. (1962) – Contribuţii privind cunoaşterea aparatului vulcanic de la Uroi. D.S.Com.Geol., XLVIII, p. 31-37, Bucureşti.

Bordea J., Berbeleac I., Borcoş M., Mantea G. & Stancu J. (1978) – Harta geologică 1:50.000, foaia 90a-Geoagiu. Institutul de Geologie şi Geofizică, Bucureşti.

ICSD (1998) – PDF-Card 41-1432, Pseudobrookite, Iron Titanium Oxide (Fe₂TiO₅)

Koch A. (1878) – Neue Mineralien aus dem Andesit des Aranyer Berg in Siebenbürgen. Tscherm.Min.Petr.Mitteilungen, 1, p. 331-361, Wien.

König U., Benea M., Göske J. & Pöllmann H. (2001) – Der Berg Magura Uroiului in Rumänien – Locus Typicus des Pseudobrookits. Der Aufschluss, 52, p. 271 - 281, Heidelberg.

Laţiu V. (1937) – Contribuţii la studiul petrografic al andezitului cu pseudobrookit şi cu incluziuni exogene de la Uroi, jud.Hunedoara. Rev.Muz.Geol.Min.Univ.Cluj, VI/1-2, p. 104-126, Cluj.

Pascu R. (1932) – Carierele şi apele minerale din România. St. tehn. ec., VI, 11, 113 p., Bucureşti.

Pîrvu G. (1964) – Carierele din RPR. Ed. Tehnică, 344 p., Bucureşti.

Rath G. v. (1880) – Mineralien von Aranyer Berg. Zeitschr. f. Kryst., IV, p. 429, Leipzig.

Roşu E., Seghedi I., Downes H., Alderton D.H.M., Szakacs A., Pecskay Z., Panaiotu C., Panaiotu C. E. & Nedelcu L. (2004) – Extension-related Miocene calk-alkaline magmatism in the Apuseni Mountains, Romania: Origin of magmas. Schweizerische Min. Petr. Mitteilungen 84, p. 153-172, Frauenfeld.

Savu H., Udrescu C., Stoian M., Călinescu E. (1994) – The quaternary quartz trachyandesites of Uroi (Mureş Valley): Petrology, geochemistry and origin. Rev. Roum. de Géol., Géogr., Géophys., série Géologie, 38, p.9-23, Bucureşti.

Traube H. (1892) – Über den Pseudobrookit von dem Aranyer Berge in Siebenbürgen. Zeitsch. f. Kryst., 20, p. 327-331, Leipzig.

Tudor D. (1968) – Oraşe, târguri şi sate în Dacia Romană. Ed. Ştiinţifică, 342 p., Bucureşti.

Udubaşa G., Strusievicz R.O., Dafin E. & Verdeş Gr. (1992) – Mineral Occurences in the Metaliferi Mountains, Romania. Rom. J. Mineralogy, 75, Suppl.2, 35 p., Institute of Geology and Geophysics, Bucureşti.

Wollmann V. (1996) – Mineritul metalifer, extragerea sării şi carierele de piatră în Dacia romană. Bibliotheca Musei Napocensis XIII. Veröffentlichungen aus dem Deutschen Bergbau-Museum Bochum Nr.63, 469 p., Cluj-Napoca.