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

New sixth generation MiniFlex X-ray diffractometer (XRD) is a multipurpose analytical instrument that can determine: phase identification and quantification, percent (%) crystallinity, crystallite size and strain, lattice parameter refinement, Rietveld refinement, and molecular structure. It is widely used in research, especially in material science and chemistry, as well as in industry for research and quality control. It is the newest addition to MiniFlex series of benchtop X-ray diffraction analyzers from Rigaku, which began with the introduction of the original MiniFlex system decades ago. Read more...

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