Dennen's Common Minerals
by Bill Shelton

If we want to make a list, it could be based on many different approaches.  Here, I am starting with an older textbook by Dennen [1960].  Rather than try to “fix” the data with a newer list of species names, I’ll try to reference the ones he used and give more recent names in some cases.  For example, Dennen lists the epidote series where we would be likely to give a list of species today that includes epidote.  You should use a new book like Back, 2016 or perhaps the IMA list which is available on your computer.  I think mindat.org might also be of some help in this regard. 

Common is at best a judgment call and we can agree or disagree about which minerals deserve to be mentioned.  As one example, Dennen lists ice which I would tend to omit because my choices will be biased toward collectible species, especially when they are likely to be available as crystals.  Isn’t that what many collectors do –whether or not they think about doing it is another issue. 

The list itself has 137 entries; of those I have deleted some because there are few examples that fill my definition of COLLECTIBLE.  Seen any nice kaolinite lately? Nor have I, so it will not be covered.  If we use his exact terminology, we find 24 minerals that are labeled as common which is about 18% of the total of 137.   about half of the total are said to be found as crystals but that does not mean all examples will be crystals.  I note three groups where the crystals are more prominent than one might realize.  They are oxides, sulfides and silicates.  We also found there are about 22 where Denned labeled them as widespread and that can matter in terms of field collecting opportunities and perhaps the likelihood of finding them for sale at a mineral show.

I think you may want to see a list of the commoner species.  They include sphalerite, the tetrahedrite series, bournonite, hematite, pyrolusite, magnetite.goethite, calcite, siderite, cerussite, barite, anglesite, gypsum, apatite series, quartz, orthoclase, kaolinite, muscovite, serpentine, enstatite series, tourmaline series, garnet group, zircon, epidote series, andalusite, and sphene.  Also, he indicates plagioclase is probably the most abundant mineral.  A few of these do not in my opinion offer much to a mineral collector; pyrolusite is not likely to be very sought after for example.  The Denned list includes a few species such as niccolite that are not of special interest to many of us. 

Crystals are a very big issue for me and perhaps a lot of other collectors.  I went through his data and added some minerals I think you can find in crystals to his list.  The results show 87 out of 137 is possible; that is 63.5%.  Good news for us!  One example is sulfur which is not indicated as a “crystal” example but I can easily convince myself that a lot of collectors would say it is easy to find in crystals and ought to be on the list. Azurite is here as well. Can you picture this species as not being a good example for crystals? 

I went to a book I have always liked: Mineralogy for Amateurs by J. Sinkankas [1964].  Clearly his focus is more aligned with collectors than mineralogy per se. on page 275, he says “ …nearly three hundred species are described.. most likely to be ..collected in the field, placed in collections, …also includes “exceedingly rare” species.. that occur in fine specimens and are eagerly sought for by the amateur’.  Perhaps we should consider his selections and bear in mind that it is a collectors list.  Many examples ie boleite and crocoite are labeled as excessively rare or very rare according to the author.  Dennen [1960] does not list boleite and mentions crocoite as an isotype [under monazite].  But then his focus is “mineralogy” rather than collectible minerals. 

Also consider the length/space given to an individual entry because Dennen gives each one basically the same space and Sinkankas varies the allotted space a lot to suggest the relative importance of one species over another.  Calcite gets 6 pages and babingtonite gets one paragraph of about ¼ of a page.  Another less precise measure is market availability.  Consider this anecdote:  one year I saw an entire room of the “very rare” crocoite and don’t recall seeing hardly any feldspars which are probably among the most common minerals.  This has a lot to do with what collectors want and are willing to buy and in no sense reflects the rarity of a given species. so, as collecors we can continue to seek out the species we like and maybe keep in mind that what we purchase may affect the availability in the future.