single macroscopic silica garden tubes were grown according to a procedure described in detail elsewhere.11 , 20 in brief , the relevant metal chloride salts ( fecl3 
 6  h2o , fecl2 
 4  h2o , and cocl2 
 6  h2o , all obtained in p.a . grade from merck ) were pressed into pellets of 13  mm in diameter and fixed at the bottom of a plastic beaker . subsequent addition of sodium silicate sol ( 1:4 ( v : v ) dilution of water glass from sigmaaldrich , reagent grade ) at a controlled rate ( 110  ml  min depending on the type of metal salt used ) produced single tubes ( length : ca . 20  mm ; diameter : ca . 6  mm ) with an end open to the atmosphere , which allowed us to draw aliquots from the inner solution at different times . in an alternative approach ( for insitu xrd measurements ) , miniaturized silica gardens were grown by placing tiny seed crystals of the aforementioned metal salts on the bottom of thin glass capillary tubes ( mark tubes from hilgenberg ; length : 85  mm , diameter : 2  mm , wall thickness : 10  m ) and slowly adding small amounts of diluted water glass ( 1:4 ) with a syringe . xas measurements were performed at the material science beamline i811 of the synchrotron radiation facility maxlab ii in lund , sweden . 10  l samples were extracted from the solution inside macroscopic silica garden tubes with the aid of ultrathin rectangular precision capillaries ( vitrocom , inner dimensions : 0.12.050  mm , wall thickness : 100  m , borosilicate glass ) , which were subsequently fixed on a holder and centered relative to the incident xray beam ( 1  mm diameter ) . the concentration of co or fe was determined without any further dilution by measuring the height of the edge jump at the fek and cok edges , respectively . calibration of edge jump values to actual metal ion concentrations was achieved by measuring a series of solutions with known concentrations in the range of 04  m , by using a fast scanning routine ( qxas mode , 100  ev to + 370  ev relative to the absorption edge , total acquisition time : 150  s ) . for all cations , a linear relationship was found for the height of the edge jump as a function of concentration ( see figure  s1 ) . iron and cobalt metal foils served for energy calibration , and gave absorption energies of 7110.75 and 7708.78  ev for the fek and cok edge , respectively . measurements with actual samples were performed by using an extended routine in stepscan mode ( 100 to + 200  ev relative to the edge , varying step width between 1 and 6  ev , with 1  s integration time per step and a total acquisition time of 600  s ) . timeresolved xrd measurements were performed in two distinct setups ( macroscopic and miniaturized growth ) by using two different synchrotron sources . macroscopic silica gardens were investigated at beamline f3 of the doris iii storage ring at hasylab ( desy , hamburg , germany ) , which allows edxrd experiments to be conducted with a white xray beam ( energy range : 652  kev ) . therefore , thick samples ( single tubes grown in duran glass tubes with dimensions of 12100  mm ) could be analyzed without the problem of total radiation absorption . the asprepared samples were inserted into a specially designed thermostatted holder ( see figure  s2 ) , equipped with two windows to allow the beam to pass through the sample . the sample holder was positioned such that the center of the glass tube was exactly at the intersection point where the incident beam hits the virtual extension of the detector arm . the intensity of the incoming white beam was adjusted by a first slit system , with an effective beam area of 300300  m . scattered xrays were detected with a ge detector ( 2048 energyselective channels , cooled with liquid nitrogen ) , which was positioned at a horizontal angle of =7 relative to the incident xray beam . a second slit system mounted on the detector arm was adjusted to an area of 100100  m or 200200  m to improve resolution . a pc coupled to a multichannel analyzer was used for data collection , and allowed automated edxrd runs to be performed with an acquisition time of 300  s per run . energy calibration was achieved by measuring the fluorescence peaks of a mixture of different metal powders . experiments with miniaturized silica gardens were carried out at beamline xrd1 of the synchrotron radiation facility elettra in trieste , italy . measurements were performed with a monochromatic beam ( e=12.4  kev , =1.00   ) , which was obtained by filtering white xray radiation ( energy range : 421  kev ) through an optical system including a doublecrystal si(111 ) monochromator set . since the overall beam intensity was not high enough to allow studies on thick ( macroscopic ) samples , silica gardens were grown in glass capillaries , as described above . the capillaries were fixed on a customdesigned sample holder ( see figure  s4 ) and positioned in such a way that the beam passed through the capillary slightly above the seed crystal , where the probability to hit the forming tubes was highest . xrd measurements were initiated directly after addition of silicate solution to the seed crystals , with an effective delay of about 3  min between completed preparation and the start of data collection . subsequently , 2d diffractograms were recorded with a ccd detector ( marresearch , image diameter : 165  mm ) , positioned at a sampletodetector distance of 60  mm , giving a final 2 range of 0106.2 referred to cuk1 radiation ( 1.54   ) . acquisition times varied from 5 to 80  s , depending on the respective beam intensity , which was determined from the actual ring current . measurements were performed repeatedly in periods ranging from 3  min at the beginning to several hours at later times . the collected 2d diffraction images were processed with fit2d software to extract 2 and intensity values from the raw files . subsequently , background subtraction , data smoothing , and integration of reflections were performed with a customdesigned labview software routine . finally , the processed data were fitted according to the proposed kinetic models by using tablecurve 2d . single macroscopic silica garden tubes were grown according to a procedure described in detail elsewhere.11 , 20 in brief , the relevant metal chloride salts ( fecl3 
 6  h2o , fecl2 
 4  h2o , and cocl2 
 6  h2o , all obtained in p.a . grade from merck ) were pressed into pellets of 13  mm in diameter and fixed at the bottom of a plastic beaker . subsequent addition of sodium silicate sol ( 1:4 ( v : v ) dilution of water glass from sigmaaldrich , reagent grade ) at a controlled rate ( 110  ml  min depending on the type of metal salt used ) produced single tubes ( length : ca . 20  mm ; diameter : ca . 6  mm ) with an end open to the atmosphere , which allowed us to draw aliquots from the inner solution at different times . in an alternative approach ( for insitu xrd measurements ) , miniaturized silica gardens were grown by placing tiny seed crystals of the aforementioned metal salts on the bottom of thin glass capillary tubes ( mark tubes from hilgenberg ; length : 85  mm , diameter : 2  mm , wall thickness : 10  m ) and slowly adding small amounts of diluted water glass ( 1:4 ) with a syringe . xas measurements were performed at the material science beamline i811 of the synchrotron radiation facility maxlab ii in lund , sweden . 10  l samples were extracted from the solution inside macroscopic silica garden tubes with the aid of ultrathin rectangular precision capillaries ( vitrocom , inner dimensions : 0.12.050  mm , wall thickness : 100  m , borosilicate glass ) , which were subsequently fixed on a holder and centered relative to the incident xray beam ( 1  mm diameter ) . the concentration of co or fe was determined without any further dilution by measuring the height of the edge jump at the fek and cok edges , respectively . calibration of edge jump values to actual metal ion concentrations was achieved by measuring a series of solutions with known concentrations in the range of 04  m , by using a fast scanning routine ( qxas mode , 100  ev to + 370  ev relative to the absorption edge , total acquisition time : 150  s ) . for all cations , a linear relationship was found for the height of the edge jump as a function of concentration ( see figure  s1 ) . iron and cobalt metal foils served for energy calibration , and gave absorption energies of 7110.75 and 7708.78  ev for the fek and cok edge , respectively . measurements with actual samples were performed by using an extended routine in stepscan mode ( 100 to + 200  ev relative to the edge , varying step width between 1 and 6  ev , with 1  s integration time per step and a total acquisition time of 600  s ) . timeresolved xrd measurements were performed in two distinct setups ( macroscopic and miniaturized growth ) by using two different synchrotron sources . macroscopic silica gardens were investigated at beamline f3 of the doris iii storage ring at hasylab ( desy , hamburg , germany ) , which allows edxrd experiments to be conducted with a white xray beam ( energy range : 652  kev ) . therefore , thick samples ( single tubes grown in duran glass tubes with dimensions of 12100  mm ) could be analyzed without the problem of total radiation absorption . the asprepared samples were inserted into a specially designed thermostatted holder ( see figure  s2 ) , equipped with two windows to allow the beam to pass through the sample . the sample holder was positioned such that the center of the glass tube was exactly at the intersection point where the incident beam hits the virtual extension of the detector arm . the intensity of the incoming white beam was adjusted by a first slit system , with an effective beam area of 300300  m . scattered xrays were detected with a ge detector ( 2048 energyselective channels , cooled with liquid nitrogen ) , which was positioned at a horizontal angle of =7 relative to the incident xray beam . a second slit system mounted on the detector arm was adjusted to an area of 100100  m or 200200  m to improve resolution . a pc coupled to a multichannel analyzer was used for data collection , and allowed automated edxrd runs to be performed with an acquisition time of 300  s per run . energy calibration was achieved by measuring the fluorescence peaks of a mixture of different metal powders . experiments with miniaturized silica gardens were carried out at beamline xrd1 of the synchrotron radiation facility elettra in trieste , italy . measurements were performed with a monochromatic beam ( e=12.4  kev , =1.00   ) , which was obtained by filtering white xray radiation ( energy range : 421  kev ) through an optical system including a doublecrystal si(111 ) monochromator set . since the overall beam intensity was not high enough to allow studies on thick ( macroscopic ) samples , silica gardens were grown in glass capillaries , as described above . the capillaries were fixed on a customdesigned sample holder ( see figure  s4 ) and positioned in such a way that the beam passed through the capillary slightly above the seed crystal , where the probability to hit the forming tubes was highest . xrd measurements were initiated directly after addition of silicate solution to the seed crystals , with an effective delay of about 3  min between completed preparation and the start of data collection . subsequently , 2d diffractograms were recorded with a ccd detector ( marresearch , image diameter : 165  mm ) , positioned at a sampletodetector distance of 60  mm , giving a final 2 range of 0106.2 referred to cuk1 radiation ( 1.54   ) . acquisition times varied from 5 to 80  s , depending on the respective beam intensity , which was determined from the actual ring current . measurements were performed repeatedly in periods ranging from 3  min at the beginning to several hours at later times . the collected 2d diffraction images were processed with fit2d software to extract 2 and intensity values from the raw files . subsequently , background subtraction , data smoothing , and integration of reflections were performed with a customdesigned labview software routine . finally , the processed data were fitted according to the proposed kinetic models by using tablecurve 2d . as a service to our authors and readers , this journal provides supporting information supplied by the authors . such materials are peer reviewed and may be reorganized for online delivery , but are not copyedited or typeset . technical support issues arising from supporting information ( other than missing files ) should be addressed to the authors .
abstractsilica gardens are extraordinary plantlike structures resulting from the complex interplay of relatively simple inorganic components . 
 recent work has highlighted that macroscopic selfassembly is accompanied by the spontaneous formation of considerable chemical gradients , which induce a cascade of coupled dissolution , diffusion , and precipitation processes occurring over timescales as long as several days . in the present study , this dynamic behavior was investigated for silica gardens based on iron and cobalt chloride by means of two synchrotronbased techniques , which allow the determination of concentration profiles and timeresolved monitoring of diffraction patterns , thus giving direct insight into the progress of dissolution and crystallization phenomena in the system . on the basis of the collected data , a kinetic model is proposed to describe the relevant reactions on a fundamental physicochemical level . 
 the results show that the choice of the metal cations ( as well as their counterions ) is crucial for the development of silica gardens in both the short and long term ( i.e. during tube formation and upon subsequent slow equilibration ) , and provide important clues for understanding the properties of related structures in geochemical and industrial environments .