THE HOLY GRAIL: LEGRANDITE FROM MEXICO

 

The latest issue of Rocks and Minerals (July/August 2020, Vol. 95, No. 4) had a great article entitled Legrandite: Ojuela Mine, Mapimi, Durango, Mexico written by Malcolm Southwood and Peter Megaw.  It tells a fascinating story about finally discovering the Type Locality (Flor de Peña Mine, Nuevo Leon, Mexico) of legrandite, the mining engineer who furnished the name (Louis Charles Antoine Legrand; 1861-1920), and stories about beautiful specimens from the more famous Ojuela Mine.  Flor de Peña Mine is a small mine without much history that essentially is only known as the Type Locality for legrandite.  My specimen was picked up at Ackley’s Rock Shop before it closed several years ago; however, at one time it belonged to Willard Wulff (1904-1998) a well-known micromounter in Colorado Springs, a Charter Member of the Colorado Springs Mineralogical Society, and a “student” of Lazard Cahn.  The Wulff name is on the micromount box and a label said, “Flor de Peña Mine, Lampazos de Naranjo, Nuevo Leon/Mexico/TYP”.” Since it was for sale in a rock shop, I suspect someone may have acquired it from Wulff and it then went to Ackley’s. I do not have the slightest idea how Wulff acquired the specimen (most likely not self-collected) except probably by trading or buying.  Another possibility might be a purchase or trade from one Louis Pardo who operated Pardo’s Rocks and Minerals in Tucson, Arizona from 1948-1972. The slight clue is I acquired a second legrandite micromount at the Wulff estate sale (a few years ago) stating it was collected from Santa Eulalia, Mexico, with the names Wulff and Pardo affixed as the label.  I presume this means that Wulff acquired the specimen from Pardo.

Legrandite is a hydrated zinc arsenate [Zn₂(AsO₄)(OH)-(H₂O)] and a very collectable specimen due to its color and rarity.  The prismatic crystals are usually a beautiful bright- to wax- yellow color (perhaps ranging to dull orange and rarely colorless) with a vitreous luster and striations. They are translucent to transparent depending on depth of color. Crystals have a conchoidal fracture and are quite brittle, so collectors are careful with mounting. Hardness has been measured at ~4.5 (Mohs). Crystals occur as singles or sprays.  Most legrandite crystals are small and less than 1.0 to .5 cm in length. Like its zinc arsenate relatives, legrandite is a secondary mineral from the oxidized zone where zinc- and arsenic- bearing primary minerals provide the metallic cations.

Southwood and Megaw (2020) describe the Flor de Peña legrandite prismatic crystals as having blunt dome and pinacoid terminations and occurring “on a dull reddish-orange brown gossanous matrix of massive to botryoidal smithsonite.”   However, I am somewhat confused as to the matrix!  The matrix on my specimen is not a ferruginous gos

 

san and is more of botryoids composed of very tiny, sparkly green crystals.  There are several photos in MinDat that are similar to mine.  For example, Jordy Fabre states: “Nice miniature with prismatic crystals [legrandite] on Smithsonite matrix that we analyzed [green].”  Robert Lavinsky has a photo of: “gem legrandite crystal rosettes are very aesthetically clustered or isolated on the undulating, layered latticework of tiny sparkly, gemmy, dark olive-greenish sphalerite crystals.”  Paul de Bondt states: “Yellow legrandite crystals on dark green smithsonite.”  I simply cannot identify these small crystals. What I do recognize is that many collectors believe legrandite specimens from the Type Locality are quite rare.

Width of specimen ~9 mm.

Legrandite crystals on tiny green crystals (see text).  Width FOV ~7 mm.  Crystals are somewhat more yellow in real life.  Best the digital camera could do with vitreous crystals.

The most widely known legrandite specimens are from the Ojuela Mine at Mapimi, Durango, Mexico.  Southwood and Megaw (2020) noted that “Ojuela mine legrandite is commonly more gemmy, more lustrous, and more elongate with prominent sharp elongate dome terminations….Ojuela legrandites are widely considered as one of the ‘holy grails’ for collectors of Mexican, if not worldwide, minerals.”  But unfortunately, I do not have a holy grail Ojuela legrandite.

The Wulff-Pardo legrandite mounted on pedestal in Perky Box.  Height ~9 mm.

Now, I also have a second legrandite specimen, the Wulff-Pardo specimen that was collected at “Santa Eulalia.”  It is a single 9 mm. spray of tightly packed, single crystals each with a flat termination, all are striated and sort of a dull orange color. Here is the problem:  Southwood and Megaw (2020) note that the “Inglaterra Mine in the Santa Eulalia District …is the final Mexican legrandite locality, although the species is only known from five or six specimens collected here in 1986.”  I am convinced that the Wulff-Pardo specimen was collected before 1986!  Is this a seventh specimen, or is the locality information on this original Perky Box mislabeled?  That is one of life’s persistent questions and far above my pay grade for an answer.

Whoa, hold the press due to a serendipitous discovery! The Free Dictionary defines serendipitous as: making fortunate discoveries while searching for other things. The heirs of a CSMS members consigned a collection of rocks and minerals to Rebecca Nohe Estate Sales, a local firm that hosted a sale today.  I was hesitant about attending due to Covid-19; however, a limited number of potential buyers were allowed in at any one time for a 30 minute viewing/purchase (by appointments only) and masks were required of all persons entering the premises.  So off I go to see the goodies and what did I notice but a specimen of the holy grail!!  Yep, a legrandite specimen in the boxes contained a number of nicely terminated crystals from Mina La Ojuela, Mapimi, Durango, Mexico.  The specimen was originally purchased from the Mineral Adit Rock Shop in Colorado Springs for $60; however, I picked it up for $4.  It is not often that collectors can have a holy grail mineral for a nice four bucks.  Wow.  So now I have legrandite specimens from all three locations in Mexico and am happy as a lark! 

  

Several photomicrographs of legrandite crystals on botryoidal smithsonite and ferruginous gossan matrix.  Prismatic crystals range from ~.5 to 2 mm.

Another one of my favorite idioms: Why do people say happy as a lark?  It simply is derived from the birdsong of the lark. When you listen to the lark's birdsong, it sounds very happy, and thus the phrase "happy as a lark.". It connotes a sort of released abandon of happiness, fully embraced and unguarded.