Woodash
Well-Known Member
Hello all -
Curiosity got the better of me and I had a look at the mineralogy of my La Veinette combo. I was unable to measure the entire bulk rock, so instead, I raised a slurry of comparable thickness (milkiness) from both the coticule and the BBW side of the hone. The slurry was air-dried and then measured using x-ray diffraction (XRD).
Mineralogy of the slurry raised from the BBW and coticule is ~similar, with the following exceptions:
1) the BBW has a higher content of (microcrystalline) quartz, mica, hematite, and chlorite, and
2) the coticule is dominated by garnet > mica > quartz with no hematite, and only minor chlorite.
The garnet content of the coticule slurry is considerably higher than that of the BBW. Note that this is for the slurry and not the bulk rock. Still, the lack of much garnet in the BBW slurry was surprising because BBW rocks are reported to have up to ~25% garnet vs. up to ~40% for the coticule (see, e.g., http://www.coticule.be/faq-reader/i...-to-a-coticule-40a-story-about-garnets41.html). The low garnet concentration in the BBW slurry suggests that it may not be the actual bulk garnet content of the hone that is important, but rather the rate at which it releases garnets to slurry. At least in the case of my combo, the coticule releases its garnets much more readily than does the BBW. The data shown here is also consistent with my own observation that it is more difficult to raise a slurry on the BBW than on the coticule – or at least it takes longer to develop a slurry of equal concentration (milkiness). This effect is probably due to the (cementing) nature of the minerals that comprise the rock matrix (higher quartz, mica, and chlorite content, and the presence of hematite in the BBW). The trace Mn-oxide phases are of little consequence here.
In any event, I show here the raw data (as x-ray diffractograms) for your own interpretation. The scan for the BBW slurry is blue (top scan) and the red scan is the coticule (note that the scans were offset along the y-axis for clarity). The positions of ‘pure phase’ quartz and spessartine peaks (pink and blue, respectively) are shown as vertical lines on the bottom of the figure. Note that even pure phases have many peaks, and that peaks sometimes overlap among multiple phases. Only spessartine and quartz are shown here so that important relationships are not obscured by other phases.
I have labeled selected peaks for garnet (G), mica (M), chlorite (Ch), quartz (Q), and hematite (H). I think you can see the higher relative quartz and mica contents in the BBW, and the near absense of chlorite and hematite in the coticule, for example. You can also see the difference in garnet content between materials, but please note that most peaks (for all phases) are attributable to more than one mineral. For example, the garnet (G) peaks at ~48.2° and ~°59.5 in the coticule are due only to garnet. These same locations in the BBW scan have only a very small peak there (only minor garnet). On the other hand, the ‘garnet (G)’ peak on the coti scan at ~42.5° is caused by both garnet and quartz, so the BBW peak at this position is due to quartz alone and not garnet.
Anyway….this is just FYI….
Curiosity got the better of me and I had a look at the mineralogy of my La Veinette combo. I was unable to measure the entire bulk rock, so instead, I raised a slurry of comparable thickness (milkiness) from both the coticule and the BBW side of the hone. The slurry was air-dried and then measured using x-ray diffraction (XRD).
Mineralogy of the slurry raised from the BBW and coticule is ~similar, with the following exceptions:
1) the BBW has a higher content of (microcrystalline) quartz, mica, hematite, and chlorite, and
2) the coticule is dominated by garnet > mica > quartz with no hematite, and only minor chlorite.
The garnet content of the coticule slurry is considerably higher than that of the BBW. Note that this is for the slurry and not the bulk rock. Still, the lack of much garnet in the BBW slurry was surprising because BBW rocks are reported to have up to ~25% garnet vs. up to ~40% for the coticule (see, e.g., http://www.coticule.be/faq-reader/i...-to-a-coticule-40a-story-about-garnets41.html). The low garnet concentration in the BBW slurry suggests that it may not be the actual bulk garnet content of the hone that is important, but rather the rate at which it releases garnets to slurry. At least in the case of my combo, the coticule releases its garnets much more readily than does the BBW. The data shown here is also consistent with my own observation that it is more difficult to raise a slurry on the BBW than on the coticule – or at least it takes longer to develop a slurry of equal concentration (milkiness). This effect is probably due to the (cementing) nature of the minerals that comprise the rock matrix (higher quartz, mica, and chlorite content, and the presence of hematite in the BBW). The trace Mn-oxide phases are of little consequence here.
In any event, I show here the raw data (as x-ray diffractograms) for your own interpretation. The scan for the BBW slurry is blue (top scan) and the red scan is the coticule (note that the scans were offset along the y-axis for clarity). The positions of ‘pure phase’ quartz and spessartine peaks (pink and blue, respectively) are shown as vertical lines on the bottom of the figure. Note that even pure phases have many peaks, and that peaks sometimes overlap among multiple phases. Only spessartine and quartz are shown here so that important relationships are not obscured by other phases.
I have labeled selected peaks for garnet (G), mica (M), chlorite (Ch), quartz (Q), and hematite (H). I think you can see the higher relative quartz and mica contents in the BBW, and the near absense of chlorite and hematite in the coticule, for example. You can also see the difference in garnet content between materials, but please note that most peaks (for all phases) are attributable to more than one mineral. For example, the garnet (G) peaks at ~48.2° and ~°59.5 in the coticule are due only to garnet. These same locations in the BBW scan have only a very small peak there (only minor garnet). On the other hand, the ‘garnet (G)’ peak on the coti scan at ~42.5° is caused by both garnet and quartz, so the BBW peak at this position is due to quartz alone and not garnet.
Anyway….this is just FYI….