Phase identification and Rietveld refinement of Connemara (Irish) marble

Connemara Marble is unique in the sense that it is only found in one place on earth - in Galway County on the scenic west coast of Ireland. Inland from this coastal region is a series of 12 mountains known as the 12 Bens. This is where the unique marble is quarried. A combination of different types of minerals is what makes this beautiful green marble so unique.

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Normally, marble is composed of a limestone (CaCO₃) mineral exposed to high temperatures and pressure causing a metamorphic change in the overall texture and appearance of the rock.

However, in addition to containing a limestone mineral (calcite), there are 3 other phases belonging to the serpentine mineral family found in Connemara Marble. The main polymorphic forms are chrysotile, antigorite, and lizardite. X-ray diffraction is a viable technique to identify and pinpoint the exact phase of the serpentine family.

Figures 2 shows the specimens of Connemara marble that were pulverized and analyzed with the Rigaku's MiniFlex benchtop diffractometer.

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Figure 2

The obtained diffraction pattern and the results of phase identification are shown in Figure 3 and Table 1.

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Figure 3


Mineral
Name
Chemical
Formula
Reference
#
Crystal
Symmetry
Space
Group
Wt
%
Lizardite Mg₃ (Si₂O₅(OH)₄) FIZ 23813 Triclinic C1 38.2
Calcite CaCO₃ FIZ 20179 Hexagonal R-3C 44.5
Chlorite IIb MgFeSiAlOOH JCS 159 Triclinic C1 15.1
Dolomite Ca(Ca0.07Mg0.93)CO₃ FIZ 152203 Hexagonal R-3 2.2

Table 1

A Rietveld analysis was performed using the model obtained from these phases and quantitative results are shown in Table 1 and Fig 4 in the form of a pie chart.

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Figure 4

The fifth generation MiniFlex is a general purpose X-ray diffractometer that can perform qualitative and quantitative analysis of polycrystalline materials. The MiniFlex is available in two variations. Operating at 600 watts (X-ray tube), the MiniFlex 600 is twice as powerful as other benchtop models, enabling faster analysis and improved overall throughput. Running at 300 watts (X-ray tube), the new MiniFlex 300 does not require an external heat exchanger. Each model is engineered to maximize flexibility in a benchtop package. Read more...

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