As Wendell Wilson wrote recently in his High End Report Tucson Show 2014  “Color is King […]” and I think most mineral collectors will agree with his statement. Even more if we are speaking about fluorite specimens!

This is the first post about how to differentiate the fluorite specimens from Asturias, Spain. Today, I will focus in the wide  colour range of fluorite crystals. In others posts I will speak about crystallization, mineral association, etc.

As you all probably know, fluorites crystals from Asturias, an small region in the north of Spain, rank between the finest cubic fluorites in the world.

There are some other fluorite localities in Spain, outside Asturias region, but they are not very well known for gemmy crystals and the quality is usually low. So we will focus only on the colour of the fluorites from the fluorspar deposits of Asturias, Spain.

Fluorite collectors from overseas usually get confused about the fluorite localities in Asturias. So many localities, so many mislabelled specimens. So this is a problem for a collector concerned with the origin of his fine fluorite specimens.

There are many obscure fluorite localities in Asturias but we will keep it simple for this post. To start with, I am going to let you know the four most famous localities nowadays. Each one produces quite different specimens, but sometimes is very difficult to assure the exact locality of a specimen.

1- La Collada . La Collada mining area comprises several fluorspar mines. Usually fluorites from La Collada range between blue and  violet, but dull green hues are not specially rare. Zoned crystals are common. It is not very difficult to find blue and violet or light blue and dark blue in the same crystal.

General note for the green fluorites from La Collada: Dull green crystals are not rare, specially in some old areas; but vivid, bright greens, are exceptionally rare. Nowadays, green coloured crystals are rarely seen in the mineral specimen market.

Note: La Viesca Mine has been worked as an open pit and underground mine. It is inside of La Collada mining area. It usually produces from very light to very dark blue – violet coloured crystals. Purple colour is uncommon. Blues with a hint of green are scarce. Small colourless crystals are common, but large ones are quite uncommon. Highly saturated light blue crystals are rare.

 

2- Berbes mining area. Blue, violet and purple fluorite crystals, being the last probably the rarest, although pure blue is not common either. As a general and easy rule I could say that the closer to the red spectrum the rarer it is.  Berbes area tends to the red spectrum (purple) much more than La Collada.

Zoned fluorite crystals in Berbes are common, but to find two different colours in the same crystal is unusual. Let me explain: You can find light purple crystals with a medium or dark purple phantom. The same stands for violet or blue. But to find a blue crystal with a purple or violet phantom is uncommon.

3- La Moscona Mine. Almost all fluorites from this underground mine are yellow. Ranging from pale and greyish yellow to honey coloured or extremely vivid yellow, being probably this last one the rarest among the yellows. Rarely, you can also find dark blue (with more or less violet – purple component)) and strong red.

Usually zoned fluorite crystals in La Moscona Mine show different shades of yellow – honey colour. Much more rare are specimens showing reddish phantoms, being the rarest the blue – yellow phantoms.

Note: Villabona Mine is a different fluorspar mine  near Moscona Mine. Based on the specimens I would say that both mines operate the same fluorspar deposit. There are only around five kilometres between the entrance of the two mines. Specimens from these two localities are very difficult to distinguish. We could say that fluorite crystals from La Moscona Mine usually tend to warmer yellows (honey, reddish), whereas Villabona tend to cooler yellows (very light hints of green).

As I mentioned before, to differentiate fluorite specimens from La Moscona and Villabona is a very difficult task, even for experts! As a very personal note, I would say that is imposible to differenciate specimens from one and other locality as a whole! You can spot specimens from one and the other, based on famous pockets for example, but everyone will fail sooner or later.

4- Emilio Mine. The most common colour in this underground mine is the lack of colour! Usually greyish and sometimes gorgeous water clear fluorite crystals. Light blue is not uncommon, being dark blue quite uncommon, but not rare in some areas of the mine. As a general rule for this mine: colours are light.

Note: Jaimina Mine is a fluorspar underground mine very near Emilio Mine. Indeed one connects or almost connects  with the other, although mine entrances are two kilometres away from each other. To distinguish between fluorite specimens from Jaimina and Emilio is practically impossible. The same “La Moscona – Villabona issue” here. Of course, you can distinguish pockets but not the specimens from either locality as a whole. As a very general and unprecise opinion, fluorite pockets in Jaimina tend to warmer blues, whereas Emilio tend to cooler blues. Could this be due to Jaimina being closer to Berbes than Emilio?

I hope you enjoyed this post. If you have any comments, ideas or suggestions please feel free to send me an email.

New photos will be added to this post in a near future. Stay tuned and sign up with us in our home page. www.spanishminerals.com

Juan Fernandez Buelga

Many of the fluorspar mines of Asturias are closed, being others active. Mineral collecting in them is forbidden by the mining companies which operate the mines and the Spanish law.

An small new find with with dark green bluish quartz crystals was found in the famous Panasqueira Mines during late 2013.

Panasqueira is well known for its superb colorless and trasparent quartz crystals (See article about the Panasqueira Mines in the Mineralogical Record Vol.45, 1 by Jordi Fabre and Carles Curto).

Well crystallized inclusions are not rare (see photo below) but coloured crystals are a novelty from this mine. At the moment it is not known which mineral causes this nice green bluish colour.

The collected specimens are associated with two different generations of what it seems to be calcite. Some of them present colorless apatite crystals and very minor sulfides.

 

Juan Fernandez Buelga

 

 

 

 

Mining began in the district in 1898 but probably the Panasqueira mines (Portugal) were first worked for tin by the Romans and next by the Moors. In 1927 the mining concessions were taken over by Beralt Tin and Wolfram, Ltd. (a british company). Today Panasqueira is one of the biggests tungsten mines in the world and it is being operated by Sojitz Coorporation, a japanese company. The Panasqueira district have indeed several mines, known as Corga Seca, Barroca Grande, Panasqueira, Vale da Ermida and smaller ones. Some of them have closed many years ago like for example Val da Ermida, this last mine produced some of the best mineralogical examples of all Panasqueira district history.

The ore deposits of the Panasqueira district are the leading source of tungsten in western Europe. The Panasqueira district is located in the Beira Baixa province about 34 km west of the city of Fundao, Portugal.

At least since 70´s the Panasqueira Mines are known among mineral collectors for the beauty of the minerals found there. In my personal opinion Panasqueira has given many of the best apatites in the world, but this mine is not only about apatites, it has produced a exceptionally large suite of other minerals that they also rank as the very best for the species. However the ammount of fine crystallized different minerals you can find in just one specimen is what sets apart this locality.

Sadly, the way mining companies have been operating this deposit does not help protecting the mineral art these mountains hide. Furthermore miners can loose their jobs if they remove minerals from the mine. Nevertheless miners risk their positions taking out a few specimens just to earn a few more euros to compesate their low salaries. These conditions plus the lack of time end up in a shortage of minerals where most of them are severely damaged. The situation is so bad that trading of minerals from the mine or visiting old mine workings is an offence, this makes Panasqueira mineral collecting even harder now..

Geology of the mining district

The surface geology of the Panasqueira district is restricted to the tightly folded vertically-dipping pelitic Beira Schist which suffered greenschist-grade, regional metamorphism during the early compressive stages of the Hercynian orogeny. Original lithologies were principally argillaceous to arenaceous shales, graywackes, and fine grained sandstones. Taken as a whole this sequence, which is widespread in Portugal, has been referred to as the Beira Schist complex.

Although no granite crops out in the district, a granite cupola (Panasqueira granite) has been identified at shallow depths in the Panasqueira mine and is at least spatially related to the mineralization. Pervasive hydrothermal alteration of the Panasqueira granite prevents its lithologic correlation with other intrusive facies of the Hercynian granitic complex exposed elsewhere in Portugal. However, from its undeformed condition and the fact that it utilized late (post-regional metamorphic) joints in its emplacement, the granite was clearly intruded after the main compressive stage of the Hercynian orogeny. Isotope studies suggest that the Panasqueira granite is an S-type granite.

Structure of mineralization

The prevailing horizontality of the Panasqueira veins is a feature of this district which sets it apart from other tin-tungsten deposits. The veins, which range in width from a few milimeters to more than a meter, cut across the altered granite cupola and steeply dipping Beira Schist thereby indicating the mineralization ocurred after emplacement and crystallization of the pluton.

Because the mineralization is open-space filling rather than replacement, this presents a special problem as to how the structures were initially dilated and then managed to remain open during the subsequent mineralization. Evidence suggests that the flat vein openings were created and supported by hydraulic pressures of the early tin-tungsten vein fluids (fluid pressures exceeded lithostatic pressures).

Mineralogy of the veins

Over fifty mineral species have been described from the Panasqueira deposits. Due to the coarse-grained nature of the minerals, the Panasqueira deposits have been known for their good mineral collecting. Although there is a rather complex paragenesis, the mineralogy is uniform laterally, composed dominantly of quartz. with lesser amounts of muscovite, topaz, tourmaline, carbonates, apatite, wolframite, cassiterite, and sulfides.

Vein paragenesis and alteration

The paragenesis is fairly complex because several minerals, including quartz, muscovite, and pyrite, were long-lived in the sequence and were precipitated in a repetitive manner. In spite of these complexities, four main stages of mineralization have been recognized and described: (1) the oxide-silicate stage, (2) the main sulfide stage, (3) pyrrhotite alteration stage, and (4) late carbonate stage. Economically, the first stage was by far the most important, because it includes the ore minerals cassiterite and wolframite.

Click here to see other high quality minerals from the Panasqueira Mine: http://www.spanishminerals.com/specimengalleries.htm

 

 

Below is an extract of the flyer written by Piritas de Navajun SL, some of the information could be outdated but still a nice text in english about the most famous pyrite cubes in the world.

The Navajun Mine

The Navajun Mine that produces exclusively pyrite crystals was discovered in 1960 by miner Pedro Ansorena Garret. Currently the mining property belongs to the company Piritas de Navajun S.L. which was formed by Pedro Ansorena Conde, Jose Chaver Atanasio and Nestor Lopez Ogalde.

Pyrite is an iron sulphide known from the early days of civilization. In the ancient China was used to attract richness and prosperity, given its metallic shine. In the old days, was used by magicians and alchemists who attributed medicinal properties to the stone. According to historians, in the La Rioja region, the stones were called “Stones of Santa Casilda”and were employed as ammunition for the rubber slings used to repel the wolves.

This “Natural Phenomena” represents the only concentration of pyrites known in the world, with an awesome perfection of cubes and group crystals of large size. Cubes with edges of up to 21 centimeters have been extracted from the mine.

The perfection and beauty of the specimens, true sculptures inspiring artists and architects are exhibited in the most important mineralogical museums of the world, such as Smithsonian Institution, Washington, USA, Germany, Switzerland, France, Japan, etc.

The origin of the pyrites talks about the decomposition of organic material in sedimentary rocks (limestones and sandstones) in a reducing environment, which generated sulphur that reacted with the iron present in the surrounding rocks. These rocks are approximately 125 – 130 million years old and were formed under the same geological environment of the Jurassic sediments present in the La Rioja region. Fossil dinosaurs tracks are commonly found in the rocks of the region.
The size and shape variation of each crystal group, the differences between the angles of the crystallisation axis of each cube and the differential growth of the various cubes, given infinite possibilities of shapes and forms. Besides the individual cube which constitute a work of art as such each specimen is different from each other.

Due to the delicate nature of the pyrites (this mineral is hard but fragile), the extraction work is conducted by hand and each sample is prepared as an individual sculpture. Furthermore, the discovery of a mineral with unique features worldwide, is a fascinating task.

Navajun village

The beautiful village of Navajun, from which the name of the mine comes, is located in the Aguilar del Rio Alhama area and was donated in 1381 by Enrique II to the Navarran Gentile Juan Ramirez de Arellano, Senor de Cameros. The donation included the villages of Aguilar Valdemadera, two beautiful villages located in the neighbourhood of Navajun.
Currently the village keeps the same features from its construction in the XVI century, occupying 16,3 square kilometres of mountainous terrain.

Besides the Mine, the resources of the village are sheep growing and cultivation of cereals. Its population has been gradually decreasing through the last century, from 310 inhabitants in 1900 to 220 in 1950, 152 in 1970 and 22 nowadays.