Monday, October 22, 2012



I grew up in geology classes with the name "sphene" firmly entrenched in my repertoire of mineral names (CaTiSiO5).  I really didn't know too much about the mineral except that study collection housed a really nice greenish crystal.  During those halcyon days of my youth I believed that all crystals in the field certainly would be almost identical to those specimens in the study collection!  Wow, that thought was one of those "non-truisms  they teach you in school" moments.
Later on in sedimentary geology class I discovered that sphene is classified as a "heavy mineral" (specific gravity 3.5+ for sphene) and may be separated (for example in sandstones), along with other "heavies" such as zircon, ilmenite, epidote, apatite, magnetite, garnets, rutile and others.  An analysis of these heavy mineral concentrations often help geologists understand the original source area for the particles in the sandstone--many heavy minerals are distinctive of a specific source area.  For example, one class project determined that the provenance for a particular sandstone was a series of metamorphic rocks a few hundred miles away---the abundance of rutile in the heavy mineral separation lead to that speculation.  Rutile is a common mineral in high temperature-high pressure metamorphic rocks.

Heavy minerals (density greater than ~2.9) may be separated from "lights" (such as quartz and feldspars) by the use of a heavy liquid such as bromoform and a centrifuge.  Further separation may be made with the use of magnetic attraction.

Rockhounds are quite familiar with mining of placer gold.  However, several other minerals form important placer deposits such as the titanium-rich ilmenite beach sands in Alaska. Cassiterite placers are important sources of tin in Malaysia and Indonesia.

Sphene is a common accessory mineral in many igneous and metamorphic rocks; however, the grains are usually small and tough to distinguish with a hand lens.  But, with the use of cut thin sections and a petrographic microscope, a whole new world opens up for the geologist.  Sphene is observable and identifiable.
My next experience with sphene occurred in the shop of a faceter who had stunning specimens of this green to yellow-green, high dispersion, gemstone.  However, these faceted specimens are mostly for exhibit since their hardness is quite low (~5-5.5) and the mineral is brittle and easily breaks.

I now look for sphene stones to examine; however, they are often tough to locate.  The faceted stones have a brilliant luster, some unique colors of green to yellow-green, and maybe even tending to a brownish-green or reddish-green.  In fact, the stones, if cut correctly, exhibit a nice pleochroism-changing colors when looked at via different angles.  A jeweler told me that some of his faceted specimens have a very strong fire especially when displayed with a brilliant cut (refractive index of over 2).  Although I have not seen such, it is my understanding that heat-treated stones will lose their "greenness" and turn red.

So, I have seen many "grains" of sphene via heavy mineral separation and thin sections but was still on a quest for one of those nice green crystals! Where would I find one?  Well, the specimen finally came to me via an unexpected route--in a flat of mixed minerals at an estate auction!  Whatever, I now have these beautiful green crystals--of titanite?  Yep.  Seems like in 1982 the International Mineralogical Association Commission on New Minerals and Mineral Names adopted the name titanite and discredited the name sphene (for its wedge shaped crystals) since the mineral has a high percentage of titanium (CaTiSIO5).  How could they do such a thing?  RIP sphene.


Post Script: I recently was able to acquire another crystal of titanite collected from Kennesaw Mountain, Georgia.  It is perched, by itself, on a mass of quartz.


  1. Thank You Sir...Considering your experience and insight i would request you to publish articles more of this kind...better publish more about the metamorphic textures studied from thin-sections, namely the chronological relationship among the minerals, prograde and retrograde features, pre-tectonic, syn-tectonic and post-tectonic features.
    Again thank You

    1. hello. Thank you for reading the post and your reply. I am just an ole paleontologist trying to cobble my way through the sometimes confusing world of mineralogy. Your projects sound interesting; however, I do not have skill sets needed for something like this. However, I do have fun with this little blog. So again, thanks for reading and good luck with your projects. mike