ORIGINAL PAPER

X-ray diffraction and SEM study of kidney stones in Israel:quantitative analysis, crystallite size determination,and statistical characterization

Vladimir Uvarov • Inna Popov •

Nandakishore Shapur • Tamer Abdin •

Ofer N. Gofrit • Dov Pode • Mordechai Duvdevani

Received: 31 August 2010 / Accepted: 25 January 2011 / Published online: 10 February 2011

� Springer Science+Business Media B.V. 2011

Abstract Urinary calculi have been recognized as

one of the most painful medical disorders. Tenable

knowledge of the phase composition of the stones is

very important to elucidate an underlying etiology of

the stone disease. We report here the results of

quantitative X-ray diffraction phase analysis performed

on 278 kidney stones from the 275 patients treated at

the Department of Urology of Hadassah Hebrew

University Hospital (Jerusalem, Israel). Quantification

of biominerals in multicomponent samples was per-

formed using the normalized reference intensity ratio

method. According to the observed phase composi-

tions, all the tested stones were classified into five

chemical groups: oxalates (43.2%), phosphates (7.7%),

urates (10.3%), cystines (2.9%), and stones composed

of a mixture of different minerals (35.9%). A detailed

analysis of each allocated chemical group is presented

along with the crystallite size calculations for all the

observed crystalline phases. The obtained results have

been compared with the published data originated from

different geographical regions. Morphology and spatial

distribution of the phases identified in the kidney stones

were studied with scanning electron microscopy (SEM)

and energy-dispersive X-ray spectroscopy (EDS). This

type of detailed study of phase composition and

structural characteristics of the kidney stones was

performed in Israel for the first time.

Keywords Kidney stones � Urinary calculi �Biominerals � Quantitative XRD analysis �EDS mapping � Crystallite size

Introduction

Urolithiasis (kidney stone disease) is a long-standing

medical illness and is still a common public health

problem. It affects up to 10–20% of the general

population worldwide (Moe 2006; Coe et al. 2005).

The knowledge of phase composition of kidney stones

is necessary for a better understanding of the nature of

urolithiasis, its etiology, for choosing the correct

treatment modality, and for preventive medical treat-

ment. According to Smith (1998), the analysis of the

kidney stones identifies risk factors leading to stone

disease and this information can be utilized to direct

therapy.

Electronic supplementary material The online version ofthis article (doi:10.1007/s10653-011-9374-6) containssupplementary material, which is available to authorized users.

V. Uvarov (&) � I. Popov

The Faculty of Natural Science, The Center

for Nanoscience and Nanotechnology, The Unit

for Nanoscopic Characterization, The Hebrew University

of Jerusalem, E. Safra Campus, Givat Ram,

91904 Jerusalem, Israel

e-mail: vladimiru@savion.huji.ac.il

N. Shapur � T. Abdin � O. N. Gofrit � D. Pode �M. Duvdevani

The Department of Urology, Hadassah Hebrew University

Hospital, 91904 Jerusalem, Israel

123

Environ Geochem Health (2011) 33:613–622

DOI 10.1007/s10653-011-9374-6

Powder X-ray diffraction analysis (XRD) and

Fourier transform infrared spectroscopy (FTIR) are

the powerful tools widely used for the identification

of crystalline phases in kidney stones. Both methods

have advantages and disadvantages. FTIR is faster

and easier to apply. But quantification of multicom-

ponent mixtures containing various oxalates, phos-

phates, and urates is rather problematic for this

method (Singh 2008; Kanchana et al. 2009) so that at

intricate phase compositions, only semiquantitative

results could be obtained. Corns (1983) emphasizes

that X-ray diffraction analysis does provide informa-

tion not given by other methods, for example,

distinguishing Ca(COO)2 • H2O from Ca(COO)2.

XRD method does not allow chemical identification

of an amorphous material of kidney stones if the

latter is present. However, the XRD method allows

calculation of chemical composition based on the

results of quantitative phase analysis. Therefore in

our opinion, for quantitative phase analysis, the XRD

method is preferable.

It is necessary to emphasize that the kidney stones

are not the simplest object for a phase analysis. The

majority of biominerals composing the stones have

low crystal symmetry (monoclinic or orthorhombic)

and rather large unit cell parameters. Therefore, XRD

patterns of their mixtures have strong overlapping of

peaks. Capabilities of different modern methods of

quantitative XRD analysis (QXRDA) to characterize

mixtures of various phases were studied by a number

of researchers (Stephenson et al. 2001; Newman and

Byrn 2003; Hillier 2000). However, similar type of

study had not been yet performed on significant

sampling of kidney stones.

It should be noted that there is no commonly

accepted agreement for the threshold phase composi-

tions under which the stone can be referred to one or

another basic type. Therefore, frequently it is difficult

to compare data reported by different researchers

(Abdel-Halim and Abdel-Aal 1999; Leonard 1961;

Fazil Marickar et al. 2009; Miller and Lingeman

2007; Bartoletti et al. 2007; Parmar 2004; Kleinman

et al. 2004; Tosukhowong et al. 2007).

In the present work, we investigated phase compo-

sition of kidney stones recovered from patients who

were treated for urolithiasis in Hadassah Hebrew

University Hospital. We classified kidney stones by the

QXRDA results, and the obtained results have been

compared with the published data originated from

different geographical regions. In addition, we applied

back-scattered electron imaging and EDS mapping in

order to study relation between morphological features

of stone and its phase composition as defined by XRD.

The relationships between mineral composition of

kidney stones and various medical aspects practically

were not considered in this work as we plan to consider

these aspects in our separate article.

Materials and methods

Two hundred and seventy-eight kidney stones were

obtained from 275 patients who were treated for

urolithiasis in the Department of Urology (Hadassah

Hebrew University Hospital, Jerusalem, Israel) in

2007–2010.

All of these stones that were either spontaneously

expelled or following procedural extraction were sent

for analysis. Samples were stored in pre-cleaned

plastic or glass vials. Prior to structural study, all the

samples were carefully washed using ethyl alcohol in

order to remove any remaining blood clots. Dimen-

sions of the tested stones varied from a few millime-

ters to 2 cm. The macroscopic shape of as-received

kidney stones was different for each sample varying

between a spherical one, an ellipsoidal or just

irregular. The majority of the studied samples were

represented by the zonal or breccia-like formations

that can be characterized by certain sequence of the

alternations or the changes of crystalline phases.

X-ray powder diffraction measurements were

performed on the D8 Advance diffractometer (Bruker

AXS, Karlsruhe, Germany) with a goniometer radius

217.5 mm, Gobel Mirror parallel-beam optics, 2�Sollers slits, and 0.6-mm receiving slit. The statistical

homogeneity and representativity of an analytical

specimen was achieved by crushing the stones down

to 3–5 mm size followed by quartering. After that,

the stones were grinded manually in an agate mortar

to a powder with grain size of about 5 micron which

subsequently was filled into a low-background quartz

sample holder. The specimen weight was about 0.2 g.

XRD patterns were recorded within an angle range of

6–66� 2h at room temperature using CuKa radiation

(k = 1.5418 A) with the following measurement

conditions: tube voltage of 40 kV, tube current of

40 mA, step-scan mode with a step size of 0.02� 2h,

and counting time of 1 s per step. The instrumental

614 Environ Geochem Health (2011) 33:613–622

123

broadening was determined using LaB6 powder

(NIST SRM 660). EVA software (Bruker DiffracPlus

2010) was used for phase identification, quantitative

phase analysis, and crystallite size calculation. In

EVA, phase quantification is performed via the

normalized reference intensity ratio (RIR) method

(Chung 1974) and a content of each crystalline phase

is calculated as:

Cið%Þ ¼ 100� ðIi=kiÞ=Xn

i¼1

Ii=ki ð1Þ

where Ci is the content of i-th phase, Ii is integral

intensity of i-th phase, and ki is corundum coefficient

(RIR) for i-th phase. The ki values for analyzed

phases are stored in PDF database.

In order to estimate the accuracy of phase content

determination, we cross-checked about 15% of sam-

ples using PCW software (Kraus and Nolze 1996) as

an alternative way for quantitative analysis. PCW

was chosen because it allows modeling of preferred

orientation which could take place at a preparation of

the samples and therefore should be taken into

account when phase content is quantified.

A value of crystallite size was calculated using

Scherrer equation:

d ¼ K � kb� cos h

ð2Þ

where d is the crystallite size, k is the X-ray

wavelength, b is the FWHM (full width at half

maximum) of the peak after correcting for instru-

mental peak broadening (b expressed in radians), h is

the Bragg angle, and K is the Scherrer constant.

Statistical treatment of the obtained results was

performed according to the recommendations of

Tobias and Croarkin (2006).

Morphology and spatial distribution of the identi-

fied phases within the kidney stones were studied

with environmental scanning electron microscope

(ESEM) Quanta 200 (FEI Company, Netherland)

operated in low vacuum mode (0.63–0.68 Torr) and

equipped with EDS detector (EDAX-TSL, USA).

Results and discussion

XRD analysis revealed the presence of 19 various

crystalline phases in the studied samples. All of them

have been identified using PDF-4 database (Interna-

tional Centre for Diffraction Data 2010). The major

identified crystalline phases were whewellite, weddel-

lite, hydroxylapatite, brushite, struvite, uric acid, uric

acid dihydrate, L-cystine. Whitlockite, newberyite,

sodium urate hydrate, ammonium acid urate, potas-

sium phosphate hydrate, and ferrowyllietite at alias

(see Supplementary Material, Table 1) have been

found out much less often. Most of these minerals

are repeatedly described in the medical and mineral-

ogical literature and are typical components of kidney

stones. A majority of the identified phases belong to

groups of oxalates, phosphates, and urates. Minor

amount of amorphous component was observed only

in a few samples. For quantitative phase analysis, we

used the values of corundum coefficients stored in

accepted PDF cards (EVA software). In a general case,

the true value of corundum coefficient could differ

from the calculated one appearing in the PDF card.

That is why quantitative results of phases analysis

obtained with EVA software which uses ‘‘estimated

corundum coefficients’’ published in PDF cards are

generally defined as semiquantitative results. But, in

our case, we cross-checked the quantification results

by using PCW software as alternative quantification

procedure. In Fig. 1, we show the comparison between

the phase content values obtained for the same samples

by two different techniques. The relative errors (i.e.

Fig. 1 Phase contents in kidney stones calculated by EVA

(Bruker DiffracPlus) versus those calculated by PCW

Environ Geochem Health (2011) 33:613–622 615

123

divergences between absolute phase content obtained

for the same sample by two quantification techniques)

were estimated by the procedure we used earlier

(Uvarov and Popov 2008). They did not exceed 9.4 and

3.8%, respectively, for low- and high-phase contents.

The examples of the QXRDA results and typical XRD

patterns obtained from investigated samples are pre-

sented in Supplementary materials.

Correctness of QXRDA results is usually estimated

by their comparison to the results obtained by other

method or by the analysis of artificial mixtures. In our

case, preparation of artificial mixes for all possible

combinations of biominerals was practically impossi-

ble, whereas alternative method for full quantitative

phase analysis does not exist. Therefore, we adopt the

value for relative errors from the published data

(Hillier 2000; Uvarov and Popov 2008; Grygar et al.

2008; De la Torre and Aranda 2003) and suggest that

it should be at the order of 2–5% for the main phases

and about 5–10% for the low-content components.

The error may be lower for the samples with rather

simple phase composition (whewellite–weddellite,

uric acid–uric acid dehydrate, whewellite–hydroxyl-

apatite, etc.) and higher for samples with intricate

phase composition (oxalates–urates, oxalates–phos-

phates, and oxalates–urates–phosphates) or with an

unfavorable quantitative proportion of minerals in a

mixture.

We systematized the whole data set of the phase

compositions obtained for all the tested samples and

divided it into several chemical groups: pure oxalates,

phosphates, urates, and rarer cystine stones. The

stones with the mixed phase composition (i.e. stones,

which contained minerals from different chemical

groups) were also allocated in separate group. Since

both applied methods give close quantitative results,

only results obtained with EVA software have been

used to organize kidney stones into chemical groups.

Then, phase compositions of the basic groups were

evaluated in more details. The results of this detailed

statistical analysis are presented in Fig. 2 and Fig. 3.

In Fig. 2, we present the occurrence of each

allocated chemical group within the whole sampling

of the tested kidney stones. Of the studied samples,

64.1% are single-phase stones or multiphase samples

composed of the phases belonging to the same

chemical group. 35.9% of the samples are multiphase,

i.e., composed of a number of crystalline phases

belonging to different chemical groups. Oxalates

(whewellite, weddelite, or their mixtures) are the most

considerable part of kidney stones in the assigned

groups. These results are in a good agreement with the

data reported by Hossain et al. (2003) for Japan, by

Chou et al. (2007) for Taiwan, and by Trinchieri et al.

(1996) for Italy. For comparison, Hossain et al. (2003)

reported about 58.4% pure stones and about 40%

oxalates. Zaidman et al. (1986) reported about 77.8%

oxalates content for Israel that is higher than our

results. But their attribution of oxalate group included

also the multiphase samples, which in our case were

separated as their own group. By applying the same

attribution, we get very similar results (77.8 and 79.1%

accordingly). Former studies on kidney stone compo-

sitions have revealed sufficiently differing frequencies

for urate stones occurrence from 4 to 39.5% (Sours and

Swift 2004). For example, Herring (1962) reported an

8.6% and Pak et al. (2003) reported a 6.4% occurrence

for uric acid stones, while Mandel and Mandel (1989)

reported a 16.5% occurrence for the stones from the

United States. We observed frequency of 10.3% for

pure urates which is not beyond the results reported in

the above-mentioned publications. Our result is in

good agreement with the data reported by Zaidman

et al. (1986) for Israel (7.8% urates in 1974–1982 and

13.3% in 1966–1974). Pak et al. (2003) reported about

2.7% cystine stones, and this is in good agreement with

our data.

Detailed analysis of the multiphase samples indi-

cates that they are referred to one of three groups:

calcium oxalate–phosphates (CaOx ? Ph), calcium

oxalate–urates (CaOx ? Ur), or calcium oxalate–

phosphate–urate (CaOx ? Ph ? Ur). As is clearly

Fig. 2 The occurrence of each allocated chemical group

within the whole sampling of the tested kidney stones

616 Environ Geochem Health (2011) 33:613–622

123

seen in Fig. 3a, the most frequently occurred multi-

phase kidney stones belong to (CaOx ? Ph) group:

26% of the whole analyzed sampling and as high as

72.4% of all multiphase samples. Cystine stones were

always documented as single-phase (pure) stones in

our study. Atsmon et al. (1963) reported that urates

have been found in 37.6% of kidney stones exam-

ined by them in Israel. Our results (10.3% pure

urates ? 7.3% (CaOx ? Ur) ? 2.6% (CaOx ?

Ph ? Ur) = 20.2%) considerably differ from this

data. Perhaps the use of different method of analysis

is the reason for this difference.

Also, we demonstrate the occurrences of phase

compositions for each of three most frequent chemical

groups of crystalline phases: oxalates (Fig. 3b),

phosphates (Fig. 3c), and urates (Fig. 3d). Consider-

ing in details the compositional data for oxalate phase

only (Fig. 3b), we conclude that whewellite is the

prevailing mineral component in this chemical

group. Pure whewellite presented in 61.3% of pure

oxalate stones, while pure weddellite stones were not

observed. The percentage of a weddellite does not

exceed 20% in 68.3% of cases. It is clean that the

whewellite/weddellite ratio changes largely. Accord-

ing to our results, oxalate stones (pure and oxalate-rich

ones (containing more than 60% of oxalates)) occur in

61.2% of cases which is sufficiently close to the reports

of stone distribution worldwide.

When composition of mineral components is

considered for the phosphate group of stones (see

Fig. 3 a The occurrence of the phase compositions for the

multiphase kidney stones. Calcium oxalates are labeled as

CaOx, phosphates as Ph, and urates as Ur. The occurrence of

each group is indicated, respectively, within the whole

sampling (upper number) and within the sampling of

multiphase kidney stones (lower number in brackets); b Occur-

rence of oxalates in different ranges of concentrations;

c Occurrence of mineral components within the phosphate

group of kidney stones; d Occurrence of mineral components

within the urate group of kidney stones

Environ Geochem Health (2011) 33:613–622 617

123

Fig. 2c), it is clearly seen that in most cases (67.4%),

such stones are pure single phase (i.e. either apatite or

struvite or brushite). Although apatite is the most

frequently naturally occurring phosphate mineral in

kidney stones, pure apatite stones are rather very rare

(only 1.7%), in contrast to struvite (6.0%) and

brushite (3.6%). Only in 7.6% of cases, more rare

phosphates (whitlockite, newberyite et al.) were

found in the samples of this group. The struvite-

apatite mixture was the most frequently occurring

when compared to other mixture mineral composi-

tions (brushite-apatite and others).

Considering the phase compositions within the

urate group presented in stones (see Fig. 2d), we find

the ordinary uric acid (C5H4N4O3) and a mixture of

uric acid and uric acid dihydrate (C5H4N4O3�2H2O)

covering most of urates (89.0%). The ratio of uric

acid to uric acid dihydrate in their mixture was

practically always around 3:1. We did not find pure

uric acid dihydrate single-phase stones. In 11% of

cases, the stones were formed of rather rare sodium

urate hydrate and ammonium hydrogen urate.

It is interesting to compare our results with data

reported for the geographical regions with similar to

Israel climatic conditions. For example, Abboud

(2008) reported the 6.7% urates among analyzed

kidney stones of patients from North Jordan, and it

well coincides with our results. Abdel-Halim et al.

(1993) reported about 24% uric acid stones and 15%

phosphate stones in samples originated from western

Saudi Arabia. These frequencies are, respectively, 2.3

and 2 times higher than our findings (10.3 and 7.7%

for urates and phosphates, respectively). Khan et al.

(2004) reported about 78% oxalates mixed with

calcium phosphate (it is in good agreement with our

data), 19% uric acid stones and 3% struvite in samples

from Riyadh (Saudi Arabia). As was concluded by

Newman and Byrn (2003), by Abdel-Halim et al.

(1993), and by Khan et al. (2004), the incidence of

uric acid stones in Saudi Arabia was found higher than

that for western countries. Statistical frequencies of

oxalates and phosphates found by us are in good

agreement with the data reported by Al-Naam et al.

(1987) for southern Iraq. Nasir (1999) reported the

data for the United Arab Emirates (oxalates-38.5%,

phosphates-11.5%, urates-11.5%, and mix-38.5%). It

is sufficiently close to our results. Dursun et al. (2008)

reported about 3% of cystine stones in the samples

originated from Turkey. It matches well our results

(2.9%). But they observed multiphase stones in 18.3%

of cases, while in our study, we found 35.9% of such

stones. It should therefore be noted that such signif-

icant differences arise not only because of natural

factors but also due to lack of coincidence in criteria

by which stones are related to specific chemical group.

The crystallite size is an important parameter, on

which sufficient attention has not been paid yet.

Crystallite size is inherently connected to the growth

conditions of the crystalline phases. That is why it

affected a chemistry of growth medium and its thermo-

dynamics, which both are defined by a metabolism of a

patient. Further, we present results of additional steps

of the samples characterization undertaken to learn

more about growth of kidney stones. In Fig. 4, we

present the histograms of allocations of the crystallite

sizes for typical biominerals. First of all, it should be

noted that we found significant differences in the

crystallite size of each mineral phase forming the

stones, while weddelite (oxylate stones) and brushites

(phosphate stones) crystals have 100 nm average sizes,

hydroxylapatite crystals were as small as 12.7 nm

average size. Important is that the observed crystallite

sizes differ by about one order of magnitude for all the

minerals, and the observed size range differs for each

mineral phase. The relative error of crystallite size

measurements has been estimated as described in our

work (Uvarov and Popov 2007) and did not exceed

12.8, 8.2, and 4.6%, respectively, for the crystallite

sizes of smaller than 10, 10–40 and larger than 40 nm.

The crystallite size of the weddellite was always more

than the crystallite size of the whewellite at their

simultaneous presence in the sample. Next interesting

fact is that hydroxylapatite always exhibited smallest

crystallite size with no relation on the presence of other

minerals in the sample. We suppose that this phenom-

enon indicates that one of the processes by which

mineral appears in the stone is its completely inde-

pendent formation. In contrast, appearance of wedd-

elite and whewellite is most likely provided by their

simultaneous growth, because these two phases form-

ing oxalate stones frequently simultaneously are pres-

ent in the sample. Brushite has the biggest crystallite

size and the smallest value of relative standard

deviation that could be understood as indication of a

unified growth mechanism by which this mineral

appears in either single or multiphase phosphate

stones. Finally, the values of average crystallite sizes

found by us for oxalates and apatite kidney stones are

618 Environ Geochem Health (2011) 33:613–622

123

in good agreement with the previously reported data of

Ghosh et al. (2009).

When kidney stones are observed visually, they

usually exhibit more or less clear zonality (concentric

layers, lamellar structure, breccia-like structure, and

other). In order to correlate these visible-layered

features with the phase composition of the tested

samples, we applied scanning electron microscopy

imaging (SEM) and energy-dispersive X-ray spec-

troscopy (X-ray microanalysis) to polished sections

of 13 stones with visually obvious layered structure.

To enhance contrast provided by observed structure

of kidney stone at electron imaging, we used signal of

back-scattered electrons (BSE) which is roughly

proportional to the square of average atomic number

of the phase and therefore gives qualitative chemical

imaging of the observed object.

In Fig. 5, we present BSE images and EDS mapping

for four chosen stones. Figure 5a shows BSE image of

polished section of urate stone with an impurity of

whewellite. It is clearly seen that concentric type layers

of this stone posses alternating bright and dark contrast

zones in BSE image that indicates presence of heavier

chemical elements within the bright areas. On inset, we

show the EDS map of Ca distribution within the same

region confirming that an indeed brighter region

contains Ca while darker regions do not. Taking into

consideration that according to XRD data, this stone

consists of two main phases—uric acid (C5H4N4O3)

and whewellite (CaC2O4�H2O), and we conclude that

Fig. 4 The allocations of

the crystallite sizes for

typical biominerals

(a whewellite, b weddellite,

c hydroxylapatite, and

d uric acid). The ranges

(nm) are indicated on

X-axis

Environ Geochem Health (2011) 33:613–622 619

123

for this case, layered morphology does correlate with

the phase composition, i.e., the stone most likely grew

through alternating chronological steps at which either

uric acid or whewellite minerals were formed. Simi-

larly, we may understand the data presented in Fig. 5b

for phosphate stone consisted of hydroxylapatite and

whewellite. The concentric type layered structure is

clearly recognized in BSE image where darker narrow

zones do not contain P while enriched with C (see C-

and P-maps in the inset). Apparently, this stone was

formed through alternating growth of hydroxylapatite

(thicker sub-millimeter zones) and whewellite (thinner

zones). Differences in visible thickness of zones could

be explained either by variation of growth duration

which was available for each mineral or by their

different growth rates. BSE image of oxalate stone

composed of a mixture of whewellite (CaC2O4�H2O)

and weddellite (CaC2O4�2H2O) is presented in Fig. 5c.

In this case, we have breccia-like structure and not a

concentric one, but still grains appearing in the image

could be distinguished by their contrast. Interestingly,

in this case, chemical sensitivity of BSE imaging was

higher than that of EDS, and therefore, no difference in

distribution of Ca and O was found at mapping. But

still, like in two previous cases, morphology of the

stone correlated with the phase content, i.e., observed

distinguishable structural features correlated of the

stone correlated to its phase composition. In contrast to

these observations, we show in Fig. 5d BSE and light

microscopy (lower inset) images of urate stone com-

posed of uric acid (95.3%) and uric acid dihydrate

(4.7%). Remarkably, this stone has strongly pro-

nounced concentric layered structure easily recog-

nized under visible light, which could not be

Fig. 5 BSE images and EDS maps of four kidney stones:

a urate stone composed of uric acid (88.2%)and whewellite

(11.8%), inset—Ca-map; b phosphate stone composed of

hydroxylapatite (92.1%) and whewellite (7.9%), inset—C- and

P-maps; c oxalate stone composed of whewellite (76.1%) and

weddelite (13.9%), inset—O- and Ca-maps; d urate stone

composed of uric acid (96.3%) and uric acid dehydrate (3.7%),

inset—C-map (upper) and light microscopy image (lower)

620 Environ Geochem Health (2011) 33:613–622

123

distinguished neither by BSE imaging nor by X-ray

mapping in SEM. This happens because chemical

composition of two coexisting minerals forming this

stone is practically identical. The only difference is one

water molecule that is far below the sensitivity of

SEM-based techniques. But optical properties of the

observed concentric layers could be utilized for

successful structural analysis. And finally, taking into

consideration the quantities of co-existing phases and

visible sizes of layers, we suggest that in this specific

case, morphology has more complicated relation to a

phase composition: each layer represents rather a

mixture of co-existing phases with different rations

and, moreover, it may contain varying degree of

porosity or microinclusions. Similar phenomenon is

well known in mineralogy (agate structure, for

example).

Conclusion

In summary, we report here the results of quantitative

phase analysis performed with X-ray diffraction on

278 kidney stones from 275 patients treated at the

Hadassah Hebrew University Hospital in 2007–2010.

The tested stones ware classified into chemical

groups according to their phase compositions. Cal-

cium oxalates are the dominating type of kidney

stones. Moreover, calcium oxalates were dominant

mineral within all the mixtures of crystalline phases.

Whewellite was the most widespread biomineral

component composing the tested kidney stones.

Within the group of phosphate stones, hydroxylapa-

tite was dominant biomineral component (about 75%

over all phosphate containing stones). Urate phase

was composed of a pure uric acid in 52.7% of the

cases, and this phase was dominating within the

group of urate and oxalate-urate stones. The relative

errors in quantification of phase content are supposed

to be about 2–5% for the main phases and about

5–10% for the low-content components.

The crystallite size was calculated for all the

observed crystalline phases using XRD data. Apatite

exhibited the smallest crystallite size among all the

detected biominerals. It indicates a derived character

of apatite in the process of kidney stones formation.

Relation between phase composition and morpholog-

ical features observed in the tested kidney stones was

studied by using BSE imaging and EDS mapping.

We suppose that extended information about spatial

distribution of mineral phases and their crystallite

size might contribute to understanding of etiology of

the stone diseases.

When compared with the previously published

data, our results show close similarity to the statistics

found for the developed countries, but they differ

appreciably from the statistics of the regions with

unfavorable environment and living conditions.

We believe that characterization approach used in

the present work may be of practical interest for the

specialists analyzing kidney stones with XRD- and

SEM-based techniques. The obtained quantitative data

about phase composition of the kidney stones can be

useful to the specialists in the study of features of the

kidney stones distribution in the different regions.

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