Breakage of quartz sand particles controlled by internal defects: model glacier studies

Breakage of quartz sand particles controlled by internal defects: model glacier studies Ken OHara-Dhand1, Sue Mclaren1, Matthew Frost2, Ian Smalley1 Stephen P.Bentley31 Giotto Loess Research Group, Geography Department, Leicester University, Leicester LE1 7RH, UK.

2School of Civil and Building Engineering, Loughborough University, Loughborough

Leicestershire LE11 3TU3 School of Engineering, Cardiff University, Cardiff CF2 3AA, Wales UKCorresponding author (kod2@le.ac.uk) AbstractQuartz silt may be produced by comminution of sand particles by glacial action.Described are the results of a series of laboratory based glacial grinding experiments designed to investigate this contention. They were designed and carried out in order to gain a better understanding of the mechanisms of the breakage of quartz in nature. In all 40 grinding experiments were conducted for different grinding times and loads. The results suggest that there might be internal controls operating in natural quartz particles which affect the size distribution and nature of the disintegration products. There could be explanations for the predominance of sand and silt- an essentially bimodal clastic universe. The deformation machine used (the Janet Wright glacier machine) has some of the attributes of a glacier but is a very simple simulation. The results from earlier experiments left a number of questions unanswered. These are:

1 what effect does the grinding ring profile have on the results and how well does it match glacial grinding in practice. For this purpose a new set of grinding rings were designed to further investigate this and 2 one special ring made which was totally different to the other 3. These remaining questions are addressed in these experiments. The same material was used as in the earlier experiments namely 2mm washed and sieved Leighton Buzzard sand. The apparatus used for all experiments was a Bromhead ring shear machine; this was adapted and adjusted for these experiments(and renamed a Janet Wright glacier machine). The results obtained appear to show that the breakage mechanism in glacial grinding is very complex and that most of the interesting phenomena takes place in the first 25% of the grinding process. However, there are still some important longer term events that relate more to the grinding of the finer material.The parameters used in the grinding were based on calculations of the height and movements of glaciers from a number of world locations. These were necessary in order to determine the scaling factors for the new experiments. Key words: Glacial grinding, Bromhead Ring shear, Janet Wright glacier machine, internal structures controlling quartz particle breakage, Leighton Buzzard Sand, silt formationIntroduction

A typical sand grain is a quartz particle with a diameter of around 500um (the official ISO 14688-1 range is 2 mm-63 m). Quartz sand is derived largely from igneous crustal rocks, usually granites of which the quartz content is typically 70% (Smalley 1966). In these parent rocks two events occur which determine the nature of the sand grains. A eutectic-type reaction delivers quartz as relatively small units distributed throughout the rock. This quartz is formed as high quartz and as the system cools turns into low quartz. The low quartz crystal structure is slightly more compact than the high quartz (caused by a change in bond angle at the oxygen atoms) so a significant tensile stress develops in the rock system. These two factors appear to determine the nature of quartz silt (Smalley & Vita-Finzi 2011). The eutectic reaction delivers a certain size range, it is an effective size control, and within this limited range of size a certain level of internal stress develops. This range of stress causes a certain range of internal deformation and controls defect formation in the eutectic quartz.This simple two stage mechanism indicates that there might be a basic bimodal size distribution of clastic quartz particles: some unbroken sand particles and broken particles controlled by defect concentration and spacing: However, for sand and silt- there are two possibly distinct populations, sand for beaches and deserts, silt for loess.Quartz sand deformation has been carried out using a modified Bromhead ring-shear machine. Wright (1995) proposed the use of this machine as a simple model glacier; it delivers a shear stress to the sample and the speed of deformation and the deforming stress can be accurately controlled. It appears to make a very convenient and reasonably realistic model glacier.Some previous tests have shown that interesting size distributions can be obtained. We have used the Wright glacier machine on 25g samples of carefully sieved and washed Leighton Buzzard sand. With improved instrumentation it is possible to follow the progress of a breakage test via measurements of vertical movements in the deformation zone, see figure 1. Particles are crushed and the system compacts.The particle size analysis for figure 1 is shown in figure 2 which corresponds to a typical loess distribution

We propose that stage 3 is simply the activation of major cracks; stage 4 is the critical deformation region where silt making occurs- and this region shows the greatest vertical movement.There is not a continuous or even range of particle sizes. In addition there are natural controls on particle production and particle size. The essential sand production mechanism seems fairly straightforward (Smalley 1966) but there has been less success in establishing the silt mode. It appears that the eutectic-type reactions in the source granitic rocks establish the first particle size control; there latent sand grains are stressed by the high-low quartz transition which produces the so-called Moss defects (Moss 1966). The eutectic size is more or less fixed (by the reaction) and the stress levels are more or less fixed by (by the size of the proto-particle) thus a certain, definable range of silt particles is produced by subsequent breakage. Silt range is defined as 2m-63m, but we detect a mode at around 30 - 40m. The major silt forming defects cause the breakage shown by lines 3 & 4 in fig.1. We propose that line 1 is simply settling, the sand grains fill the sample container; line 2 is dilatant expansion (the same sort of dilatant expansion required by Smalley & Unwin (1968) in glacial till for drumlin forming purposes); line 3 is initial breakake, caused by a few major cracks; line 4 is a critical region- the Mosds defects are activated and real silt formation begins; line 5 the system is filling with detritus but a bit more deformation occurs as the system now moves towards the comminution limit. SHAPE \* MERGEFORMAT

Fig.1 Vertical displacement plotted against time, and the changing gradients indicate changes in the style of deformation. There is a wide range of sizes of clastic particles in crustal materials but there does appear to be some basic modalities. There is a sand mode, and there is a silt mode. Bimodality has been produced in earlier experiments (Smalley 1963, Smalley & Rogers 1994) but these were uniaxial compression tests and the product interfered with the process. In the Wright glacier machine the process continues and a more realistic end product is reached.

ResultsThe particle size analysis for figure 1 is shown in figure 2 which shows evidence of peaks at 2 - 3, 20 and 40m as shown by the arrows. Similar profiles has been observed from a location in south east Kazakhstan, see figure 3 and also from the Ruma brickyard near to Novi Sad in Serbia, see fig4. In particular note the peaks in similar positions to those in figure 2 with one additional peak at around 0.2 m. The reason for these double peaks is not yet fully understood and is currently under investigationFigure 5 shows the results of a run with a 36 slot ring and 24 hour grinding time, to be noted and increase by a factor of three in the number of slots and a grinding time of 24 hours. The particle size distribution for this run is shown in figure 6 which clearly shows with the increased number of slots and grinding time the material is now well into the silt region with an increased volume %. This is to be expected and can be assigned to lines 5 and 6 on figure 5 and takes place over the period 10 24 hrs.

Fig.2 particle size analysis of the results in figure 1 clearly indicating three particle size modes are produced. Evidence of peaks at 40, 25 and 2.5m

Figure 3 Particle size analysis of young loess from Remisowka SE Kazakhstan. After Machalett

Figure 4 Particle size distribution from the Ruma brickyard. Maximum ultrasonic agitation applied. Note the additional peak at 0.2m SHAPE \* MERGEFORMAT

Figure 5 Vertical displacement plotted against time for the 36 slot ring. The changing gradients indicate changes in the style of deformation.

Figure 6 Particle size analysis of the results in figure 5. Note here the shift of the particle range into the fine silt region

Figure 7Results for variable 12 slot grinding ring.

Figure 8 Particle size analysis of the results in figure 7. Note here there is a further shift of the particle range into the silt region compared to figure 6

Figure 9 Six hour run using the variable 12 slot rings again clearly showing well defined stages in the grinding process.

Figure 10 Particle size analysis of the results in figure 9. Note the shift of the particle size range from coarse sand towards the fine sand range. Figure 5 is a good example of the breakage sequence and suggests a series of actions. Here we propose that line 1 is dilatancy ; line 2 is initial crack activity; line 3 is major silt production; line 4 shows activity after most of the defects have been activated and utilized; lines 5, 6 and 7 are post-defect activity leading to the comminution limit at 1-2 um. Fig.6 and fig.8 show the results of very long term grinding; this would be very intense glacial activity leading to a very small product(and not often encountered). We suggest that a lot of natural activity occurs around the line 3 zone and results in the 3oum silt which makes estuaries and loess deposits.

Fig 10 clearly shows that modest grinding can leave sand remaining. However, the main peak is seen to be at 85 micro-metres rapidly falling to 200 micro-metres with evidence of a small amount of material below 100 200 micro-metres. This process is seen to take place over the period of slopes 1, 2, as seen in figure 9. This is classified as the sand production stage. This 6 hr run compares very well with fig 7 which was with the same grinding rings but over 24 hrsDescription of apparatus and methodThe main component of the glacial grinding apparatus is the Bromhead Ring Shear machine/ Janet Wright glacier machine shown below in figure 9. A detailed view of the grinding chamber is shown in figure 10. The vertical displacement transducer can be seen to the right near to the top of the figure. The two horizontal stress rings can be seen to the left and right of the apparatus equally spaced either side of the vertical displacement system.

Figure 11 Overall view of the Bromhead Ring Shear

The Bromhead grinding chamber is shown in more detail in figure 11A pair of grinding rings fit into the upper and lower sections of the grinding chamber. The lower chamber is set to rotate at a range of speeds determined by the setting of two gears, the range of possible speed are given in table 1. For all of these experiments a grinding chamber rotational speed of 60( per minute was chosen which is the maximum possible, see table 1. In addition a constant grinding load of 30 kg was used for all experiments with all specimens e ground wet to simulate the grinding process at the bedrock base of a real glacier.In figure 9 the upper platen rotates and the upper one is constrained by two horizontal proving rings with dial gauges and two linear variable differential transducers which measure the forces during its operation. The vertical displacement is measured by a vertically mounted (lvdt) with a resolution of 10 m. This proved to be extremely valuable when analysing the grinding data, Shown also is the space in which the grinding material was placed

Figure 12. Detailed view of the Bromhead grinding chamber

.Table 1. Gear setting for turret rotational speedsBromhead Turret rotation setting. Deg/Min

Gear leverGear settings

PositionLHSRHSLHSRHSLHSRHSLHSRHSLHSRHS

60305436454536543060

A6045302015

B129.06.04.03.0

C2.401.81.200.800.6

D0.4800.360.240.1600.12

E0.0960.0720.0480.0320.024

Details of grinding rings.The grinding ring shown in figure 12 has 36 slots of width 1mm and depth 0.6mm, the material used is M3 stainless steel.The remaining three grinding rings have 12 and 24 slots of the same width and depth and one with 12 variable width slots with the same depth with spacing of 1, 2, 3, 4, 5 and 6 mm. Theses slots were all equally spaced in the same manner as in figure 12. The reason for this was to determine the effect of different size slots on the grinding process.

Figure 13 36 slot grinding ring (one of a pair).

For reference the ISO ranges of particle sizes are shown in figure 6. From inspection of this table it can be seen that the starting material for these experiments is classified as coarse sand.Table 2 List of ISO14688-1 particle sizesISO 14688-1

namesize range

Very coarse soilLarge boulder, LBo>630 mm

Boulder, Bo>200 630 mm

Cobble, Co>63 200 mm

Coarse soilGravelCoarse gravel, CGr>20 63 mm

Medium gravel, MGr>6.3 20 mm

Fine gravel, FGr>2.0 - 6.3 mm

SandCoarse sand, CSa>0.63 - 2.0 mm

Medium sand, MSa>0.2 - 0.63 mm

Fine sand, FSa>0.063 - 0.2 mm

Fine soilSiltCoarse silt, CSi>0.02 - 0.063 mm

Medium silt, MSi>0.0063 - 0.02 mm

Fine silt, FSi>0.002 - 0.0063 mm

Clay, Cl0.002 mm

Grinding procedureAs all previous grinding experiments had been conducted with washed and sieved Leighton Buzzard sand, the same material was used in these new experiments. The amount of sand used is 25 g and is carefully placed in the lower platen (grinding chamber), see figure 9. The lower platen is then placed in the Bromhead apparatus and is held in position by two retaining screws. The top grinding platen is then carefully placed on top of this. The desired speed of rotation is the set by the adjustment of two gears, see table 1.A set of tables was designed to in order to determine the forces acting at the base of a glacier. The calculations were from a maximum depth of 3km down to 1m in steps of 1 metre. However, the maximum load that could be was 35kg, this represents 3kg on the Bromhead weight hanger, which has a lever system with a magnification factor of 10. In order not to run the apparatus at maximum load, and risk problems, a lower value of 30 kg was chosen. Table 3 is a section of the more complete tableTable 3 Glacial depths and forces on the baseHeightForce on the base of the glacierForce on ring surface

mkgNkNkg

108480.083188.8083.1933.92

97632.074869.9274.8730.53

86784.066551.0466.5527.14

75936.058232.1658.2323.74

65088.049913.2849.9120.35

54240.041594.4041.5916.96

43392.033275.5233.2813.57

32544.024956.6424.9610.18

21696.016637.7616.646.78

1848.08318.888.323.39

Table 4 Data of a number of glaciers

GLACIERLOCATIONTHICK. (m)% B. SLIPMovement (m/yr)

ALETSCHSWITZER.13750200 -85

TUYUKSURUSSIA5265?

ATHABASCACANADA3227525

ATHABASCACANADA2091025

BLUEUSA26920*

MESERVEANTARCTIC8001.7

With icefall can reach 300m/yTo gain an idea of the scaling factors for glacial movement the distance the grinding ring moves in one hour is determined. To determine this distance the average distance of 85 mm to the centre of the grinding is taken. Therefore average distance is 85 mm x ( = 267.0 mm. In one rotation at 60( per min total distance travelled is 267.0 x 6 mm - 1602 mm. or 1.602 m per rotation.Table 5 Distance travelled, in the grinding chamber of the Wright glacier machine, per unit time

Time (hrs)Distance travelled (m)

116.02

696.12

24384.48

DiscussionThe outcome of these grinding experiments was remarkably revealing as regards the vertical displacement data in which was seen very important stages in the grinding process, figures 1, 4 and 6Fractures initiate and propagate from points of critical pressure, such as grain - grain contact (Zhang et al. 1990). Empirical observations of the resulting cone-crack patterns have been observed using glass beads and rock discs (Gallagher et al. 1974), conglomerate pebbles (Gallagher, 1987; McEwen, 1981),and sand grains (Chuhan et al., 2002; Gallagher et al., 1974, 1974). Moss (1966) in a classic paper described the initial fluviatile fragmentation of granite, this gave rise to the term Moss Defects. The exact nature of these defects is not yet fully understood but there is no doubt they play an important part in the glacial grinding process. It is realized that the transition of high to low quartz played an important role in quartz breakage mechanisms and in part is responsible for the results gained.The depth and movement of glaciers is a complex process and involves many factors due to the climate variations over the last glacial period, these are discussed in detail see (Kukla 2002). Sediment production in high altitudes has been discussed by (Owen et. al 2002 and these experiments bear out there finding However, in these glacial grinding experiments and number of carefully calculated assumptions have had to be made such as the slope of the glacier had to be compensated for by precisely controlling the grinding speed. The maximum load that could be applied to the surface of the sand in the grinding chamber was 30kg. Fowler 1989 described glacial surges but it was not easy replicate this in the apparatus used.In the light of experience serious clogging of the 1mm slots was observed and it takes a considerable time to remove the debris from them. This in turn gave rise to further damage However, the variable slot grinding ring proved to be valuable in deciding what would be the best slot width to use. Therefore to avoid making up a new set of grinding rings, which would be costly and time consuming, it was decided to modify the 24 slot ring to have 2 mm and 3mm alternating slots. This modified pair of grinding rings will be used for all future experiments.The results obtained clearly show the stages of the grinding process and was reproducible as seen by the slopes shown in figures 1, 5, 7 and 9. This is considered to be an important finding as it is now clear to see up to six stages of the grinding process in at least three separate experiments e.g. slope 2 figure 1, slope 1 in figure 4 and slope 1 in figure 6 are all very similar taking into account the different profiles of the grinding rings and the different grinding times. Results of remaining experiments showed a similar pattern.The particle size distributions for the three experiments clearly show the effect of the number of slots on the grinding ring and the time of the experiment. Further work is in hand a to develop a mathematical theory of the results shown in this paperConclusions.The key question was: is there a set of internal defects in natural quartz crystals which affect the formation of clastic particles? Are sand and silt distinct entities controlled by material nature rather than by external processes? The Wright glacier machine allows us to appreciate that there are stages in the grinding process and that characteristic products are produced. Fig.5 can be presented as showing seven stages of deformation but might be better considered as showing two major stages; stages 2 and 3 constitute a loess silt forming stage where 30-40um particles are formed. Stages 4,5,6 and 7 are grinding towards the comminution limit and will eventually give a very fine product, as shown in fig.6. We tentatively propose two grinding regimes; a modest grinding to produce loess sized particles, say around coarse silt size, and a much more thorough grinding to produce very fine particles. Large scale continental glaciers might produce the very fine product which could go to form the post-glacial clays , the sensitive soils sometimes known as quickclays(see Cabrera & Smalley 1973). Large scale mountain production (as in Owen et al 2002) with smaller(but widespread) glaciers involved might tend to produce the larger silt product. What might be called early-stage grinding gives loess sized particles; late-stage grinding gives a very fine product and provides material for quickclays and similar post-glacial soils.Acknowledgements. We thank Mr Geoffey Hennell and his collegues at the Engineering Society in Ruddington, Nottingham who organised and oversaw the manufacturing of the four new grinding rings.. The quality and precision of their work was outstanding.We would also like to thank the technical staff in the laboratories of the Loughborough University School of Civil and Building Engineering for the help and assistance in running these experiments, in particular Mr. Mike Smeeton for his help with the data logging software and Mr. Jonathan Hales for his help with the grinding samplesReferencesBlenkinsop, T.G., 1991, Cataclasis and processes of particle size reduction: Pure and Applied Geophysics, v. 136, p. 59-87.Chuhan, F., Kjeldtad, A., Bjorlykke, K., Hoeg, K., 2002, Porosity loss in sand by grains crushing- experimental evidence and relevance to reservoir quality: Marine and Petroleum Geology, v. 19, p. 39-53.den Brok, S.W.J., 1998, Effect of micro=cracking on pressure-solution strain rate: The Gratz grain-boundary model: Geology, v. 26, p. 915-918.

Cabrera, J.G., Smalley, I.J. 1973. Quickclays as products of glacial action: a new approach to their nature, geology, distribution and geotechnical properties. Engineering Geology 7, 11-133.Fowler A. C.1989 A mathematical theory of glacial surges SIAM J. APPL. Math. Vol. 49. No. 1. pp 245 -263

Gallagher, J.J., 1987, Fractography of sand grains broken by uniaxial compression, in Marshall, J.R., ed., Clastic particles; scanning electron microscopy and shape analysis of sedimentary and volcanic clasts: New York, Van Nostrand Reinhold Company, p. 189-228.Gallagher, J.J., Friedman, M., Handin, J., and Sowers, G.M., 1974, Experimental studies relating to microfracture in sandstone: Tectonophysics, v. 21, p. 203-247.Jefferson, I.F., Jefferson, B.Q., Assallay, A.M., Rogers, C.D.F., Smalley, I.J. 1997. Crushing of quartz sand to produce silt particles. Naturwissenschaften 84, 148-150.Kukla G, J et. al 2992 Last Interglacial Climate. Quaternary Research, 53, pp 2-13Kumar, R., Jefferson, I.F., OHara-Dhand, K., Smalley, I.J. 2006. Controls on quartz silt formation by crystalline defects. Naturwissenschaften 93, 185-188.Moss, AJ, 1966: Origin, shaping and significance of quartz sand grains. J. geol. Soc. Aust., 13, pp. 97-.136

Moss A J 1966 Initial Fluviatile Fragmentation of Granitic QuartzJournal of Sedimentary Research Volume 42 (1972) Owen,L.A, Derbyshire ,E.,. Scott, C.H. 2002 Contemporary sediment production and transfer in high-altitude glaciers. Sedimentary Geology 155 (2003) 1336

Pro Natura Center Aletsch, Great Aletsch glacier CH-3987 Riederalp; w.w.w.pronatura.ch w.w.w.pronatura.ch/aletsc h ;

Smalley, I.J. 1963. Compaction of buried sands. Nature 197, 966967.Smalley, I.J. 1966. Formation of quartz sand. Nature 211, 476-479.Smalley, I.J., Unwin, D.J. 1969. The formation and shape of drumlins and their distribution and orientation in drumlin fields. Journal of Glaciology 7, 377-390.Smalley, I.J., Rogers, C.D.F. 1994. One dimensional high pressure compaction of granular media. Journal of.Geotechnical .Engingeering.ASCE 120, 1102-1105.Smalley,I.J., Vita-Finzi, C. 2011. A size control for quartz silt (making particulates at planetary surfaces). Central European Journal of Geosciences. 3, 37-38.Wright, J.S. 1995. Glacial comminution of quartz sand grains and the production of loessic silt: a simulation study. Quaternary Science Reviews 14, 669-680.

Zhang, J., Wong, T.-F., and Davis, D.M., 1990, Micromechanics of pressure induced

grain crushing in porous rocks: Journal of Geophysical Research, v. 95. B1, p. 341-352.List of figures

1 Vertical displacement plotted against time, and the changing gradients indicate changes in the style of deformation. .2 Particle size analysis of the results in figure 1 clearly indicating three particle size modes are produced. Evidence of peaks at 40, 25 and 2.5m3 Particle size analysis of young loess from Remisowka SE Kazakhstan.4 Particle size distribution from the Ruma brickyard. Maximum ultrasonic agitation applied. Note the additional peak at 0.2m5 Vertical displacement plotted against time for 36 slot ring. The changing gradients indicate changes in the style of deformation. 6 Particle size analysis of the results in figure 5. Note here the shift of the particle range into the silt region. 7 Results for variable 12 slot grinding ring. 8 Particle size analysis of the results in figure 7. Note here the shift of the particle range into the silt region.

9Six hour run using the variable 12 slot rings again clearly showing well defined stages in the grinding process10Particle size analysis of the results in figure 5. Note here the shift of the particle range into the silt region11Overall view of the Bromhead Ring Shear12Detailed view of the Bromhead grinding chamber

1336 slot grinding ring (one of a pair).

List of tables

1 Gear setting for turret rotational speeds2 List of ISO14688-1 particle sizes

3 Glacial depths and forces on the base4 Data of a selection of glaciers5Distance travelled, in the grinding chamber of the Bromhead apparatus, per unit time

1

2

3

4

5

6

7

6

5

4

3

2

1

1

2

3

4

5

1

2

4

6

5

3

EMBED Excel.Chart.8 \s

75 mm

100 mm

1

2

3

4

PAGE 1

_1408802955.xlsChart1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0.000032

0.00083

0.006

0.022

0.051

0.091

0.14

0.21

0.29

0.39

0.51

0.63

0.75

0.88

0.99

1.09

1.17

1.23

1.26

1.28

1.28

1.27

1.27

1.26

1.27

1.28

1.31

1.35

1.41

1.48

1.57

1.68

1.79

1.93

2.1

2.29

2.51

2.75

3.01

3.32

3.68

4.05

4.37

4.61

4.76

4.85

4.95

5.06

5.12

5.02

3.83

2.04

0.49

0.051

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

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0

Particle size (microns)

Volume %

Run 1 12 slot grinding ring

Glacial gr_run_01_01.$ls.XLS

LS7/3/08 12:42

File name:Glacial gr_run_01_01.$ls

File ID:Glacial grind

Sample ID:run 1

Operator:SMcL

Bar code:

Comment 1:

Comment 2:

Instrument:LS 230, VSM Plus

Run number:1

Start time:7/3/08 12:38

Run length:91

Optical model:Sediments 1.rfd PIDS included

Obscuration:8

PIDS Obscur:52

Obscuration:OK

Serial Number:5966

From0.04

To2000

Volume100

Mean:20.07

Median:18.49

Mode:37.97

S.D.:14.16

Variance:200.6

C.V.:70.56

Skewness:0.407

Kurtosis:-0.904

d10:2.476

d50:18.49

d90:40.89

ChannelChannelDiff.Cum.