CHARACTERISTIC BANDS. 



6 7 



spectra of supposedly related silicates is not due to a fault in the criterion 

 for judging such relations. The reflection bands of the various silicates 

 examined are represented by lines in fig. 46. The lines broken at the top 

 indicate that the reflection bands are not well resolved. The silicates of 

 the divalent metals, R "-silicates, are metasilicates, while the R m -silicates 

 are orthosilicates, as noticed on a previous page. Since there is a band (at 

 10 //) in common with both groups we are at liberty to assume that the 

 division into ortho- and meta-silicates is not a characteristic in the spectra. 

 Again, the groups of chemically related minerals may or may not have 

 similar spectra. Thus, the pyroxenes and micas have dissimilar spectra. 

 Serpentine and deweylite (and the feldspars) have similar spectra. Ortho- 

 clase and microcline, which are isomeric, show their structure by their 

 dissimilar spectra. The amphibole seems out of place. Spodumene, talc, 

 serpentine, deweylite, apophyllite, microcline, albite, and muscovite have 

 a group of atoms in common, which causes a band at about 9.7 p.. Am- 

 phibole, topaz, microcline, albite, tourmaline, natrolite, datolite, and beryl 

 have a group of atoms causing a band at 10 y.. 



Serpentine, deweylite, topaz, and albite have a common radical causing 

 a band at 10.5 y.. Quartz glass, datolite, orthoclase, and possibly amphi- 

 bole, have a band in common at 8.8 \i. 



The group of triplets in willemite, topaz, and zircon is unusual, the 

 maxima being, on an average, at 10. 1, 10.6, and 11 //, respectively. In 

 willemite (R 11 ) the bands are sharp and well defined, in topaz (R 111 ) the 

 bands are not so well resolved, while in zircon (R) the bands are almost 

 indistinguishable. Whether this change in sharpness of bands is due to 

 the variation in valence is a pertinent question. Previous work indicates 

 that the variation in the sharpness of the bands is due to the amount of 

 oxygen present oxygen sharpens the bands. In crystalline quartz and 



Table III. 



Compounds having the 

 following groups. 



CH 2 order CH 3 



NH 2 



CeHe 



N0 2 



OH 



NCS 



R-SO4 1 



R-SiOx 



R-CO3 1 



Show characteristic absorption and reflection bands at: 



3-43 



2.96 



3-25 



7-47 



2-95 



4-78 



4-55 



3 



6-5 



8.68 



6-5 

 8.8 



11. 4 



14 



9.8 



8.2 



9-7 

 14 



11.8 



8.7 

 10 

 29.4 



M 



12.95 



9.0 

 10.5 



9.2 

 11 



1 The position of the maxima in these compounds depends upon the atomic weight of the basic element, R, 

 with which the group or acid radical is combined. 



