The Rodeo District

 The small city of Rodeo is situated about 130 km to the north of the city of Durango. Near to Rodeo are located numerous epithermal vein systems. Many mineral specimens from the state of Durango are coming from this area. The most important places, where mineral specimens for collectors have been found include: Navidad mine, Patoni and the abandoned El Realito mining district.

Navidad Mine

 The Navidad mine is producing fluorite and is located 35 km to the NW of Rodeo. Fluorite veins strike NW-SE over a length of about 2 km, vein width varies between 1 and 10 m. The wall rock is principally rhyolite/rhyodacite. The fluorite in those veins is massive banded and generally does not form crystals, its color is green and purple. There exist also narrow veins with quartz and fluorite parallel to the main veins. The fluorite from those veins forms sometimes very nice purple or pink octahedrons sitting on chalcedony. Another mineral of interest for collectors from the Navidad mine is creedite. It appears in beautiful crystal aggregates or crystal balls. The creedite crystals are up to about 3 cm long, transparent colorless or slightly included with red or orange color. Creedite was formed in a late stage of epithermal activity, fluorite was etched or resolved during this stage. 

El Realito

 The abandoned El Realito mining district is situated about 10 km to the west of Rodeo, near the village of Yerbabuena. Numerous mines exploited in the past gold, silver, lead, zinc, fluorite, antimony and tungsten from vein and stockwork deposits. The mineralized area is about 6 km long and 4 km wide. The host rocks are of andesitic composition from the “Lower Volcanic Sequence” (about 25 to 35 Ma old). Currently there exist no active mines, however it is possible to find still very nice specimens of adularia, hubnerite and especially fluorite. Fluorite from El Realito forms cubes and octahedrons with crystals up to 4 cm across. Colors include apple-green, purple and white.

Patoni

This is a summary from the following articles:
Jurgeit M. (2004) - Les extraordinaires macles de calcite de Patoni, Durango, Mexique. Le Règne Minéral, vol. 59, Sept.- Oct. 2004, p. 37 - 41
Jurgeit M. (2005) – “Die Calcit-Fundstelle Patoni im Bundestaat Durango, Mexiko” in “Mineralien Welt”, Bode Verlag, 16. Jg., Heft 2, pages: 48-55.

 The small village of José Maria Patoni  (the local people name the village only Menores de Arriba) is located 35 km to the south of Rodeo. In late 2000 a local farmer made an extraordinary discovery while exploring for optical calcite (Iceland spar). He found a calcite vein with superb water-clear long-prismatic calcite crystals and butterfly twins of world-class quality. 

 The epithermal activity related to the veins with Iceland-spar in northern Durango is very young, from geologic evidence it is estimated that most of those calcite veins formed 0.5 m.y. ago or later, but they could be as young as 10,000 years.
The calcite vein near Patoni is situated at an elevation of about 1700 m in a hilly, broad valley. The massive and thickly bedded host rock is a rhyolitic unwelded ash flow tuff with up to 20 cm thick intercalated beds of fluvial conglomerate and reworked tuff. There exist at least two veins striking approximately North-South and one narrow vein trending East-West. In the main vein (the westernmost) the course crystalline calcite fills an irregular net of fractures and pockets in the host rock over a width of about 3 m. Single veinlets or pockets are up to 80 cm wide, open cavities are abundant and here the desired calcite crystals are found.

The Patoni calcite location with view to the north. Photo taken in March 2004

Cavity in the calcite vein with large long-prismatic calcite crystals, image width is 50 cm (2002)

The calcite mine is now (2004) about 9 m deep. From the surface to a depth of 3 to 6 m the faces of the calcite crystals exhibit strong  surface etching, caused by the attack of slightly acidic descending surface water. Those etched crystals are sometimes very attractive, looking similar to icicles, however often these etched crystals are covered with slightly yellow cryptocrystalline carbonate and some white opal.

 The calcite appears mainly as perfectly transparent, gemmy, colorless crystals with many faces. Sometimes very fine inclusions form milky zones. Few and far between are crystals exhibiting nicely banded zones of inclusions, the colors of those milky zones vary between white, yellow and light-brown. The inclusions consist in wall-rock particles, ranging in size from submicroscopic to sand-fraction.  Rare are transparent crystals of light-yellow color. There have been found long-prismatic crystals up to 20 cm length and “butterfly twin” + “axe-head twins” with a width of up to 14 cm. Noteworthy is also the intense phosphorescence especially after activation with short wave UV light, but it even works with strong normal light. The calcite continues to glow strongly with white light for about 15 to 30 seconds (after the light source has been removed). Fluorescence under UV light is also white and not very distinctive.

 In the “butterfly twins” two calcite individuals join with and angle of 127.45º. The twin plane of this contact twin is {0 1 –1 2}.Only two large axe-head twins have been recovered at this location. The twin law of this contact twin is after the rhombohedron plane {1 0 –1 1}, both individuals join with an angle of approximately 90º.

The “Mackita pocket” found in March 2004. This cavity filled with
calcite butterfly twins was about 80 cm long and 25 to 40 cm wide.

View into the “Frog pocket” (March 2004). This cavity was about 1.4 m long and up to 45 cm wide.
The largest butterfly twin (10 cm wide) of this pocket is intergrown with a prismatic calcite crystal
and is partly visible in the lower center of this image.