Table 6. Quantitative ICP-OES results for the investigated samples of M4, M5 and M6 (in p.p.m. by weight).

Most of the measured elements are below the limit of quantification (LOQ).

Sample	Al	Ca	Ti	V	Cr	Mn	Fe	Zn
M4 (at about 1/3 of the crystal length)	10 ± 0.03	6	<1	<2	<1	<0.3	8 ± 0.40	<0.8
M5 (at about 1/3 of the crystal length)	<3.1	9 ± 0.17	<1	<2	<1	2 ± 0.05	10 ± 0.23	<0.8
M6 (close to the end of the crystal)	<3.1	5 ± 0.02	<1	<2	<1	0.7 ± 0.07	<2	<0.8