Double Your Pleasure, Double Your Fun
I’ve known about iron cross twins for a long time. It occurred to me that it was after many years of being a collector before I ever saw one. And while I have field-collected pyrite I have not found an iron cross twin. Occasionally I have found an iron cross twin specimen at a micro mineral dealer, but it was only last year that I found one at a general rock and mineral show.
I learned of iron cross twins from mineral related reference material. For example, if you check the Mindat home page for pyrite https://www.mindat.org/min-3314.html, and scroll down a little to the “About Pyrite” section, there is a panel with 8 photos of pyrite – and one is of an iron cross twin. The description of pyrite in Sinkankas’ Mineralogy for Amateurs also mentions iron cross twins. So, a quick check of some common reference materials shows iron cross twins included even in these brief overviews describing pyrite. This relative “prominence” given to iron cross twins in common reference materials made me think that they were relatively common. But are they?
How common or rare are iron cross twins?
One way to determine this is to see how many collectors have them in their collections. I have several but then I focus on pyrite in my collection and have actively sought them out so my collecting habits in this regard are not typical. But many, many collectors have pyrite samples in their collections. After all it is one of the more popular collectable minerals. But how many have an iron cross twin? Do you? Feel free to let me know one way or another in the comments.
Another way is by looking at public collections such as museums. I’ve visited many museums but have not made notes about whether they have an iron cross twin on display. I’m sure many if not most mineral museums do. But even then, that is not the full picture as museums display only a fraction of their collections. It might be interesting to find out the number of iron cross twins compared to total number of pyrite specimens or total mineral specimens in the collection
Checking other collections, private or public, is a challenging, time consuming task that would be hard to complete and certainly not very doable during the pandemic. I decided one thing I could do is check on how common iron cross twins are by looking at Mindat. Mindat.org/ is a fantastic online resource for collectors. Aside from being a community of collectors and experts, it is a database of minerals, localities, and photos. With time on my hands recently, I thought I’d do some Mindat surfing.
Mindat currently records over 300,000 mineral localities and over 1 million photos, truly a wonderful resource! However, Mindat has some limitations. I’m sure there are photos of iron cross twins that have not been uploaded to Mindat. And I’m sure there are localities not included in Mindat that have produced iron cross twins. Despite this, I think it is useful to search Mindat as the site does capture a lot information about minerals and localities from over 50,000 registered users.
Well, Are Iron Cross Twins Common Or Not?
The Mindat data, while incomplete, is substantial in volume and allows us to draw some conclusions. I found around 75 photos of iron cross twins on Mindat out of approximately 9,000 photos of pyrite. This represents 0.83% of all pyrite photos on the site. I also found iron cross twins at about 25 locations out of approximately 42,000 localities where pyrite has been reported. This represents just under 0.06% of the localities reporting pyrite.
The Mindat data suggests iron cross twins are rare. This is consistent with general observations I’ve made about public collections and mineral shows. Further, you have probably seen flats and flats of pyrite specimens at shows – flats filled with shiny cubes from Spain, octahedra from Peru and other pyrites from around the world. But how many iron cross twins have you seen alongside them? While rare, it is more difficult to determine how rare iron cross twin are. Let’s leave that to ponder for another time.
To see more iron cross twins, check out my Mindat article https://www.mindat.org/article.php/3872/PYRITE+-+Iron+Cross+Twins
To see Part 1 click here https://pyritemania.com/2020/05/27/pyrite-matters-iron-cross-twins-part-1/