The mineralogists who work at the museum have been practising mineral identification by eye for many years, but most of the 5,636 known mineral species won’t give us their names that easily. There are two techniques using X-rays that can be employed to give our eyes some help.  

Simply put, a mineral is a solid with a long range crystal structure (the way the elements are arranged) and a fixed chemical composition (the ratios of these elements). We can use both of these characteristics for identification. 

Coloured polygons representing the crystal structure of the mineral schizolite.
Crystal structure of the mineral schizolite. The different coloured polygons represent groups of atoms and the balls represent sodium atoms. Image: Aaron Lussier © Canadian Museum of Nature

We can determine the chemical composition of a mineral by collecting X-rays while firing a beam of electrons at it. If we arrange the X-rays by wavelength, we get a spectrum showing which elements are there and, based on the height of the peaks, how much of each there is. 

Spectrum showing the X-ray peaks of a columbite-(Mn) sample. Yellow peaks on a blue background.
X-ray spectrum of columbite-(Mn). Each peak represents a different chemical element, the height of which corresponds to the amount of that element. Image: Glenn Poirier © Canadian Museum of Nature

The columbite-tantalite group minerals all look very similar; it is impossible to identify them without knowing their chemistry. There were drawers full of unnamed columbite-tantalite mineral specimens in the museum’s collection. By taking tiny samples—often smaller than a tenth of a millimetre—and analysing their chemistry, we now know the proper names for these minerals for the first time since they were acquired by the museum! 

Cabinet drawer containing twenty black specimens of columbite-tantalite, each in a separate cardboard box.
A drawer in the museum’s mineral collection filled with unidentified columbite-tantalite group minerals. Image: Glenn Poirier © Canadian Museum of Nature
Black sample of columbite-(Fe) in a cardboard box with the words “columbite-tantalite” crossed out and replaced with “columbite-(Fe).”
Mineral specimen CMNMC 48946 has its proper name after 37 years! Image: Glenn Poirier © Canadian Museum of Nature

The second technique mineralogists use to identify minerals is X-ray diffraction, also known as XRD. If we hit a sample with a beam of X-rays and record how they are affected by the crystal structure, we can get a “fingerprint” of the mineral.

Red rectangle with multiple yellow partial rings.
An X-ray diffractogram showing the pattern of X-rays diffracted off a mineral sample. Each partial ring is a diffraction from a specific crystal plane and the ring’s brightness is the strength of that diffraction.  Image: Ralph Rowe © Canadian Museum of Nature

If we use a database to compare “fingerprints” to other examples, we can identify visually indistinguishable specimens, such as serandite and schizolite. 

Vertically oriented orange sample of serandite with white crystals of analcime.
A world-famous specimen of orange serandite from Mont Saint-Hilaire, Québec. The white crystals are analcime. (specimen CMNMC 37124). Image: © Michael Bainbridge
Sample of schizolite with radiating orange blades.
For many years, the mineral schizolite was considered an obsolete name for the mineral serandite. However, a recent study by museum researchers using XRD and chemical analysis reinstated schizolite as a mineral species, in addition to showing that many of the beautiful specimens of serandite in our collection were actually schizolite, including this one from Mont Saint-Hilaire, Québec (specimen CMNMC 46265a). Image: © Michael Bainbridge

Knowing the proper names of minerals is important for any museum collection. Chemical analysis and X-ray diffraction are two important ways mineralogists keep our own collection in order and make sure every specimen is properly identified.