| 21. | They resemble leucite in their shape, but have not yet been proved to have its crystalline outlines.
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| 22. | The former consist mainly of plagioclase, leucite and augite, while the latter contain olivine in addition.
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| 23. | By far the greater number of the rocks which contain leucite are lavas of Tertiary or recent geological age.
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| 24. | They are rich in leucite, but contain also some sanidine and often much nepheline with hauyne or nosean.
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| 25. | The leucite-tephrites and leucite-basanites of Vesuvius and Somma are familiar examples of this class of rocks.
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| 26. | The leucite-tephrites and leucite-basanites of Vesuvius and Somma are familiar examples of this class of rocks.
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| 27. | Rocks that contain leucite or nepheline, either partly or a wholly replacing felspar, are not included in this table.
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| 28. | The leucite tinguaites are usually pale grey or greenish in color and consist principally of nepheline, alkali feldspar and aegirine.
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| 29. | The leucite is often present in two sets of crystals, both porphyritic and as an ingredient of the ground mass.
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| 30. | Nepheline decreases in amount as leucite increases since the abundances of the two reflect the Na : K ratio of the rock.
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