Page 1.

d(Å)	I(%)
3.86	12
3.035	100
2.845	3
2.495	10
2.284	18
2.095	18
1.927	5
1.913	17
1.875	17
1.626	4
1.604	8
1.587	2
1.525	5
1.518	4
1.510	3

In the diffraction pattern collected, the intensity of the peaks at 2.28 and 1.510Å are larger than expected (29 and 4% respectively) and the large FWHM values (0.43 and 0.42° respectively) suggests there are peaks belonging to other phases with these d spacings and intensities relative to CaCO₃ of 11 and 1 respectively.


(ii)  Normalising the remaining intensities relative to the most intense peak (with d spacing of 3.343Å) gives

d(Å)	I(%)	FWHM(°)
4.27	34	0.27
3.343	100	0.30
2.742	14	0.35
2.503	2	0.36
2.458	12	0.22
2.284	13	0.43
2.237	5	0.23
2.128	10	0.23
2.102	7	0.35
1.980	5	0.23
1.939	2	0.37
1.817	18	0.22
1.700	6	0.35
1.672	7	0.23
1.659	2	0.24
1.541	14	0.23

(iii)  Choosing the next 3 highest intensities with d spacings at 3.343, 4.27, 1.817Å and searching the Hanawalt manual gives SiO₂ (card number 5-490) (phase 2.). The card shows peaks with d spacings of 1.541, 2.458, 2.284, 2.128, 1.672, 2.237, 1.980, 1.659Å belong to this phase.

d(Å)	I(%)
4.27	35
3.343	100
2.458	12
2.284	12
2.237	6
2.128	9
1.980	6
1.817	17
1.672	7
1.659	3
1.541	15

(iv)  Normalising the remaining intensities gives

d(Å)	I(%)	FWHM(°)
2.742	100	0.35
2.503	17	0.36
2.102	50	0.35
1.939	17	0.37
1.700	42	0.35
1.510	10	0.42

(v)  Choosing the 3 highest intensities with d spacings of 2.742, 2.102, 1.700Å and searching the Hanawalt manual gives MgCO₃ (card number 8-479) (phase 3.). The card shows that all these peaks belong to this phase.

d(Å)	I(%)
2.742	100
2.503	18
2.318	4
2.103	45
1.939	12
1.769	4
1.700	35
1.510	4

(vi)  In the diffraction pattern, the patterns of the 3 phases overlap at only two d spacings (2.284Å for phases CaCO₃ and SiO₂ and 1.510Å for phases CaCO₃ and MgCO₃). The background level in the diffraction pattern masks the weaker peaks for the MgCO₃ pattern. The fact that there are no other unaccounted peaks implies that all the phases present have been identified.