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Improving Mindat.orgMineral groups from Haliburton/Bancroft

8th Feb 2010 17:30 UTCMichael J. Bainbridge Expert

I've been thinking recently about tidying up some of the duplicate locations and other problems associated with the "Bancroft collecting area" (which spans, and confuses, several political/geographical divisions - I'll make another post about that), but in doing so I found what I think might be a bigger problem: rampant (and usually incorrect) assumptions about individual species identification in photos of common mineral groups.

There are others, but the worst offenders are the amphiboles. I know everybody wants to think they've got something sexy like fluororichterite, or magnesiokatophorite, but the problem is that you might, in fact, have several species present in any given specimen from the area. Now, the good news is that most of the posts are from a relatively small group of members, so it would be fairly easy to tidy it up with their help and co-operation.

I think the best approach here would be to try to combat in-accuracy, rather than try to encourage accuracy. In an area where we have a lot of field collecting, and visual identification of common groups is impossible, I would much rather see a field name like biotite or hornblende, or a group name if necessary, than have people guess at a species.

There are, no doubt, several photos of specimens which have been positively identified (or there is other good reason to have labeled it 'X'), but this should be noted in the description, as the safe assumption upon viewing a photo of a field collected amphibole is that this identification is a guess - an innocent and well intentioned guess, mind you, but quite possibly wrong. I'm less inclined to get persnickety about a location where there has been a fair amount of study done (like the Bear Lake Diggings), but again, this should be noted.

Any thoughts?

Michael

8th Feb 2010 19:14 UTCJolyon Ralph Founder

Perhaps the term "bancroft colleting area" is unnecessary.

And I agree about renaming things to amphibole group.

Jolyon

8th Feb 2010 20:48 UTCMichael J. Bainbridge Expert

I agree about the Bancroft Collecting Area, actually referred to as the "Bancroft District" in the db - see my other post here: http://www.mindat.org/mesg-7-171670.html

For the amphiboles, to avoid there being just one long list of "amphibole group", I'd be okay with the following generalizations (based on my experience in the area, and that of several experts I've spoken to - and to apply only to the visual appearance of amphiboles here):

The name hornblende is used as a field identifier (perhaps incorrectly, and perhaps only locally, but ubiquitously) to refer to any otherwise unidentifiable black, or close-to-black (assumed to be iron rich) amphibole.

Anything bladed and/or light coloured and/or transparent is almost assuredly in the tremolite-actinolite series.

Anything that doesn't clearly fit one of the other two descriptions is amphibole group.

Any objections?

8th Feb 2010 23:28 UTCJohn Duck

I have to agree that I have seen a number of mineral identifications for the Bancroft area that were obviously mis-identified, but I think before we label everything generically i.e."amphibole", etc., we take into consideration the prior work and referenced literature on a site as regards to the species present. For instance, the Earl farm and Regional Road (Fleming Road) sites have been previously identified as fluororichterite. The Grace Lake roadcut on Burleigh Road has identified tremolite (dark green), diopside (light green), and stevensonite (earthy coating) based on existing literature. I don't think we should reinvent the wheel for such sites.

Where literature identifying the minerals present is lacking then I agree a conservative approach to identification should be used until actual testing identifies the species. I basically agree with your premise; I am just concerned that we don't get into a requirement that all species be laboratory identified.

9th Feb 2010 02:18 UTCReiner Mielke Expert

I think the term Bancroft area is useful in that it is a well know location and many specimens out there are simply labeled Bancroft, Ontario. The boundaries of nthe area are somewhat arbitrary, but as long as the township is given as a sublocality it is not a big problem. However, I think some sort of general agreement needs to be made as to how far from Bancroft something can be, yet still be in the Bancroft area.

One thing that I think we should try to stay away from as much as possible is attaching localities to towns or lakes since the locality may not be in the same township or even county as the town or lake. A good example is Wilberforce which is in Monmouth Twp. but most of the nearby mines are in Cardiff Twp. However if a specimen is simply labeled Wilberforce, Ontario and one cannot determine which mine it came form, then it would be good to establish a Wilberforce area locality. The question then is should that be a sublocality of the Bancroft area?

As for grouping amphiboles etc. since one cannot tell many of them apart visually who is to say that a specimen labeled fluororichterite is not fluororichterite? It is good to have a general category that a person can place a specimen in that is not analyzed such as Hornblende, but I wouldn't worry too much about samples that already have a more specific name attached to them unless obviously wrong.

9th Feb 2010 02:40 UTCMichael J. Bainbridge Expert

You're right John, there has been a lot of good work done at certain sites and that should be respected, and I agree with your concern - as a matter of practicality, some generalizations should be made. Also, just to be clear, I'm only talking about photo identification changes where there is no good reason to believe it is a particular species - NOT about changing referenced species entries in the location db.

A word of caution about the literature & amphiboles, however: just because a species identification has been made in one place, it doesn't mean it's the only species present, or that every amphibole that looks like it is the same. It's not uncommon to find "zoned" amphiboles that grade through several species from the core to the rim. You can have several species in the same pocket (although they may look the same), and if you go 100 feet in any direction from the study area, all bets are off. You just never know with amphiboles, especially around here.

For example, I recently had some analyses done of some material from the Fluororichterite Road-Cut, and it turned out just to be a fluorine-rich richterite. An esoteric distinction, I know, but I can't label it fluororichterite anymore, even though it's from "the fluororichterite road-cut". I don't mean to suggest that there hasn't been vast quantities of it found there, just that without analysis, there's no guarantee that what you found is. Then in another location, where only edenite had previously been identified, analysis found my samples to be nearly pure fluororichterite. And there are analysed samples of both fluororichterite and edenite from the Earle farm in the National collection.

Sorry, I've got a bit of a bee in my bonnet about fluororichterite - long story... The short version is that there have been a lot of analyses done at numerous locations around here, but few (if any) of these were ever intended to be comprehensive studies from which broad assumptions should be made. I have found (from reading the literature, and speaking to many of the people who wrote it) that much of what is assumed to be common knowledge about these sites is often based only on a few very localized findings - which is not safe to do with amphiboles.

Okay, that was a lot of words of caution. Gotta love hornblende!

9th Feb 2010 03:14 UTCMichael J. Bainbridge Expert

Reiner, my concern about the amphiboles is mostly with the numerous field collected entries. Anything with a label from a reputable dealer, or an experienced collector who is familiar with the area should probably be left alone, but if an inexperienced collector wanders off into the woods somewhere near the Millar mine and posts a photo of something black as "edenite" because that's what the guidebook said, my thinking is it should probably be changed to hornblende.

Another example of concern, however, is the Miner's Bay occurrence. We have both actinolite and tremolite listed with only the user's photos as reference. I am quite familiar with the occurrence, and most of the people who have collected there. You can easily find someone who will swear it's one or the other because so-and-so said, but the only actual analysis I've been able to find is in the collection of the Canadian Museum of Nature which indicates the presence only of one (Sorry, I forget which, I'll have to check). In this case I would be inclined to change the other, unless the poster has more than anecdotal evidence to go on.

In any event, when it comes down to individual cases, I think the poster should be contacted (and much research done) prior to arbitrarily changing their entry.

9th Feb 2010 16:34 UTCJohn Duck

Michael,

I agree; amphiboles are maddening, partly due to the better analytical techniques available. The pendulum in mineralogy seems to swing between lumpers and spliters. Lumpers preferring hornblende and spliters preferring fluororichterite, magnesiokataphorite, etc. I think the spliters are winning, but it makes it maddening when you want to be accurate.

9th Feb 2010 21:11 UTCMichael J. Bainbridge Expert

Maddening, indeed! In the end, it will have to be a judgement call for each photo, and each location. Some should be assumed to be one thing, and others should not be assumed at all. It'll require more research, and more input, but I'm glad to hear that so far everyone's agreed that it can be tidied up, and that hornblende's okay (where necessary).

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