The Fluoro-richterite Road Cut, near Wilberforce, Ontario, Canada

 

by Michael Walter


           

Phlogopite  Fluor

 


Fantastic specimens containing large crystals, in matrix and right along site the road! How could that be? Ontario, Canada boasts numerous sites such as this. The one I will describe here also has an interesting mineral called fluoro-richterite. It may sound exotic but simply stated it is a member of the hornblende family that is rather rare. In fact, it appears that this is one of the few locations for the mineral which includes two locations in the Chelyabinskaja and Sverlovskaja Provinces in the Ural Mountains of Russia, one of which is the type locality for the species.  The mineral also occurs several kilometers to the south west at Tory Hill in the Monmouth Township of Ontario.  The crystals are usually well formed, attractive and readily available to the collector who is willing to put in a moderate amount of effort to find them.

I first found out about this mineral collecting site in the early 1980s when attending the Bancroft, Ontario Mineral Show.  The town of Bancroft bills itself as the mineral collecting capital of Canada and does a great job of catering to mineral enthusiasts.  The Chamber of Commerce sells collecting guides and maps and even has a first class display of specimens from the region’s mines and collecting sites.  At this annual show specimens from all over the world are sold by indoor dealers and less formal tailgaters outside the building.  Within several miles of Bancroft there are literally tens of sites to find minerals which may be both common and exotic.  At one of these mineral shows I observed these crystals which at that time were often labeled as hornblende, fluor-richterite or fluorrichterite.  The inventory of many of these dealers included the dark gray/ black crystals of fluoro-richterite in sizes from thumbnail to large cabinet and they were noted as coming from the town of Wilberforce which is to the north of Bancroft. 

This species owes its unusual name to the effort being applied to reclassifying the group of minerals collectively called, amphiboles.  The mineral name that many of us grew up with, hornblende, is now defunct and it has been recognized as numerous species instead of just one.  Many of these new minerals are being given names based on their chemical composition which makes matters confusing.  Fluoro-richterite is a sub-member of the amphibole family.  It is a sodic-calcic clino amphible with a chemical formula of Na(CaNa)Mg5Si8O22F2.  Previously known as fluorichterite and often also spelled, fluororichterite (pronounced the same way but spelled without the hyphen); the name of this mineral is no longer in question.  Fleisher’s Glossary of Mineral Species, 2014, does not list fluorichterite or fluororichterite but does list fluoro-richterite.  Papers have been published on fluoro-richterite as recently as the late 1990s and a web search will find many sources using the name freely.  The problem is that there are even more sites, museums, universities and mineral dealers, many highly respected by specimen mineralogists, which still use the outdated names fluor-richterite and fluorrichterite.  What a mess!

 

In any case, these monoclinic crystals are strongly prismatic and have a hardness of 6 on the Mohs scale.  They are a rich gray/ black color and have lusters ranging from glassy to somewhat waxy.  At this location they will not be confused with other species because they are the dominant mineral at the outcrop with no other similar species being present.       For those who prefer to silver pick their specimens these crystals are not expensive at mineral shows but they can be on mineral web sites, especially those which profess the species to be fluorrichterite and note the Wilberforce site to be the only locale in the world where this mineral can be found.  As a result specimens range from just a few dollars to many thousands of dollars depending on the source.

Upon seeing this mineral in the early 1980s I immediately wanted to field collect my own specimens.  Collectors in the area were happy to provide directions to the site where these crystals were being found and to provide information on how to retrieve good specimens.  I was quick to make the trip to find out for myself what it was like to find fluoro-richterite near Wilberforce.   

Several miles outside the town of Wilberforce, Ontario, Canada is a calcite deposit which contains the superbly formed crystals of fluoro-richterite. These opaque crystals are scattered about within this flesh colored massive calcite. The crystals can get quite large, up to 30 centimeters in length and are usually well formed and terminated.  The terminations themselves can be one of two types.  One form is flat while the second is more complex with numerous faces creating shallow terminations.  On a rare occasion the termination will give away the presence of twinning.  Twin crystals will be quite obvious showing well defined reentrant angles on the prism faces and sometimes even on the terminations of the crystals.  Found both in the solid calcite matrix or within the surrounding soils the crystals of fluoro-richterite are common.  Because they have formed as floater crystal in the calcite they are almost always doubly terminated and if collected properly, almost always damage free.  As individually isolated crystals or in clusters they are equally attractive. 

Almost as popular as the fluoro-richterite crystals are the smaller crystals of phlogopite mica that also occur at the site. These terminated books can be translucent when viewed with good back lighting. Their color then appears to be a wonderful red. Well formed, small crystals can have a fantastic red glow uncommon to this species of mica. The fluoro-richterite and phlogopite often grown together in clusters.

Over the years many tens of thousands of specimens have been removed from this site so collecting can be great or poor depending on the methods you use.  The road cut once had enormous amounts of massive calcite, which is also fluorescent, containing crystals exposed above the level of the roadway and large expanses of soil in which to find loose crystals.  Now the site has been worked down to the point where the majority of the exposure is below the level of the road and there is little soil to exploit.  Lots of work is usually required because the easy pickings are long gone.  The remaining soil can produce specimens but the calcite produces the best material. This calcite is nothing short of bullet proof. Even drilling and sawing the rock will only produce mixed results. I have had days here that were a bonanza and others when I basically got skunked. If you do visit this popular site you might be happily surprised by your results. Bring your heavy tools such as chisels, spring steel, and sledge hammers and be prepared to work.  If you are going to work the soil you will want to have a shovel and screen.

The primary digging area can be found on the south side of the road almost across from the intersection with the Sunset Cottages Road.  There are relatively few tailings due to the fact that collectors take these in order to remove the crystals within them at home.  On the opposite side of the road you will see where the calcite seam extends there, as well.  This side of the road however, is seldom collected from because the calcite body is far narrower and tightly locked within the surrounding crystal poor country rock.

I remember visiting one summer many years ago when I was planning on only digging with simple hand tools.  An older gentleman and his wife from Michigan arrived later and started working the site with a different approach.  He had found a centimeter wide seam running parallel to the surface of the outcrop below a large slab of calcite.  He managed to establish several large wood splitting wedges into the crack and worked very hard for at least two hours pounding them into the opening with his sledge hammer.  Eventually this enormous area of land began to lift free of the outcrop.  Although it could not be moved further the block could be broken in to smaller and then again into even smaller chunks which could be hauled away.  He asked for assistance with this task and I was happy to help.  As chunks were broken crystals within the calcite could be seen with great frequency.  Having helped him to lift the large block and subdivide it he insisted I also take some of this material home to etch out the fine crystals of fluoro-richterite.  We each took as much as we dared load into our vehicles. 

At home the process of transforming these blocks of rock into crystals specimens could be approached in two manners.  The first was simple.  Like other durable crystals found in calcite these could be etched free using hydrochloric acid.  The second method I find more preferable and that involves chipping away areas of the calcite from around the crystals by exploiting the calcite’s strong cleavage.  A tiny chisel and hammer are used to take off small pieces until the desired amount of crystal is exposed.  Dental tools can also be helpful for this task.  This method is risky and often results in damaged or totally broken crystals but it can also result in fine specimens left in matrix which do not have the unnatural appearance of those which are partially etched using acid.  Whichever method is used the goal is to expose as much of the fluoro-richterite as possible.  Crystals standing out in high relief from the calcite matrix also tend to be more aesthetic.  Those collectors who are interested in fluorescent specimens will be happy to know that the calcite does have a nice red fluorescence under short wave ultra-violet light.

This site has been a popular location for at least three decades.  As a result there has been extensive collecting on what was initially a small geologic occurrence.  What was once a small hillside directly by the road on the edge of the Earl farm property has been leveled off by collectors from all parts of the world who have come to gather examples of the fine minerals found there.  The collectors have been aggressive to say the least.  Many have even employed hammer drills and rock saws to work the calcite in their retrieval of specimens.  The easy collecting is over but there is still ample opportunity to fine attractive specimens of fluoro-richterite and phlogopite at the road cut.  Collecting quality specimens in an easily accessed location is becoming a rare opportunity for today’s mineral collectors.  So, if you find yourself looking to add some well formed crystals to your collection don’t be afraid to stop by the fluoro-richterite road cut near Wilberforce, Ontario, Canada.  You will be glad you did.

Directions:

At the intersection of route 648 and route 4 in the town of Wilberforce turn left onto route 4 and travel for 3.2 km to where the Sunset Cottages Road intersects route 4 from your right (the north).  The road cut is approximately 50 meters further west on route 4 on the south side of the highway.  Be sure to keep safety in mind when digging at this location.  The hill on which the site is found has poor visibility so you will want to be sure and park well off the road or on the nearby Sunset Cottages Road.  There is a campground in the town of Wilberforce as well as access to fuel and food.  Stop by the Bancroft Chamber of Commerce for directions to this and many other sites in the immediate area. Good luck.

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