Rutile type locality, Horcajuelo de la Sierra, Community of Madrid, Spaini

Regional Level Types
Rutile type locality	- not defined -
Horcajuelo de la Sierra	Municipality
Community of Madrid	Autonomous Community
Spain	Group of Countries

Metamorphic outcrop with rutile-bearing metamorphic segregation veins in mica schists. This locality consists of a set of many different locations such 'Dehesa de la Cabezada' (the classic outcrop), 'Cerro de las Cabezuelas' (or 'La Dehesilla'), 'El Lanchar', 'El Frontil', 'Las Losillas', 'Rodeo del Lomo' and of course the surroundings of 'Arroyo de las Cabrillas'.

Rutile was described as a mineral species by Werner in 1803, from specimens purportedly from "Cajuelo, Vuitrago, Burgos". It is clear that this was an error, and the actual locality for the specimens studied by Werner was Horcajuelo de la Sierra (Madrid), where their existence had already been known as a curiosity, although not scientifically described, since well before. Consequently, Horcajuelo de la Sierra (Madrid) is the real type locality for this mineral. (The cause of Werner's erroneous reference to Vuitrago (Buitrago) may have been the historical fact that Horcajuelo belonged to the Señorío de Buitrago, from the Duques del Infantado until the abolition of the residual feudal regime in 1830).

The rutile specimens that were found spread in the soil at 'Mata de la Cabezada Hill' (Horcajuelo de la Sierra) had attracted the attention of local people during ages. They were called 'acerillos' (small steel pieces). Early mineralogists in the XVIIIth century identified them as red schorls. Herrgen (1799) reproduced the analytical data that Klaproth had published before in 1797 about the rutile specimens at this outcrop, one of the first locations to be studied in the world; he indicated 'Mata de la Cabezada Hill' as the locality for these specimens, a hill 'a quarter league' (1.5 km) from the village. These locations supported old mines that were called 'Pozos de los Moros' (Wells of the Moors) by Herrgen contemporaries where silver was obtained according to him. Rutile is found in one of the hillsides, the same with the 'pozos'; it appears spread in the soil from the basis of the hill. Specimens can occasionally be found nowadays but it is really difficult after several centuries of collecting. Rutile appears always as loose crystals, usually as rounded pebbles, sometimes with some massive quartz matrix, but this is not a primary outcrop. Single prismatic crystals with heavily longitudinal striation up to '3 inches long x 1.5 inches wide' (Herrgen 1799). Herrgen (1799) described also their 'constant tendency to join', that is twinning, and he reported twinned groups up to four members.

Lévy (1837a) pointed out some rutile specimens (single crystals and twinned groups) from this locality in H. Heuland collection. Twins (geniculated and cyclic) are even more frequent than single crystals.

(Ancient references in Calvo 2009, op. cit. below)

Other Regions, Features and Areas containing this locality

References