My apologies for the slight blogging hiatus over the last little while. I have been preparing for a conference and then attending and so I had to put blogging on the back seat for a few weeks to prepare properly. However, the conference is done, my talk is given so now I can get back to blogging…at least until the next one…which starts on Tuesday (tomorrow). Luckily, I get to just watch at this one and don’t have to go through the effort of actually preparing to say anything. This conference is a very focused and small event that specifically concerns the geoscience of the proposed low-level radioactive waste storage facility in the Bruce Peninsula.
The photo for this week is known simply as the “The Candelabra”. It is one of the best if not the best specimen of blue-cap tourmaline in existence.
Blue cap elbaite at the Smisthonian Museum in Washington D.C. (Photo: Matt Herod)
Of course, the Canadian Museum of Nature has a pretty nice one also:
Blue cap at the Canadian Museum of Nature (Photo: Matt Herod)
Both of these unbelievable specimens come from the same location, which is the Tourmaline Queen Mine in Pala, California. The mine is still a producing gem mine to this day and if you would like to find out about its colourful history click the link above (pun intended). The geology of the mine is no less fascinating than the crystals it produces. It is located in a pegmatite, which is a class of igneous rock that can often be a source of large crystals and/or unusual mineralogy. Pegamatites are a type of intrusive igneous rock that can form from a melt that contains a high percentage of volatiles, such as water, which lowers the viscosity of the melt and allows for the formation of large crystals compared to those formed from a higher viscosity melt. Some crystals can be several metres in length. Furthermore, pegmatites can often contain a high concentration of incompatible elements such as lithium, tungsten and boron. These elements, among others, don’t normally form minerals easily, and are known as lithophiles or incompatible elements. When they are forced to crystallize in a pegmatite that has branched off a large batholith the result can often be unusual minerals such as toumaline or spodumene.
The reason that the tourmalines from the Tourmaline Queen have the “blue cap” is because of their chemistry. In the case of the blue caps there is a sudden shift from manganese rich to iron rich, which causes the sudden change in colour.
Thanks for reading,
Matt
p.s. This post represents something of a milestone for this blog as it is my 50th post since this blog began in October 2012. I am looking forward to another 50!
