theralite การใช้

• Theralite is the intrusive equivalent of nepheline basanite, a foidal basalt with essential calic plagioclase and essential olivine.
• With the increase in silica ( SiO 2 ) and the concomitant reduction in nepheline, theralite becomes gabbro.
• The discovery of theralite was looked forward to with interest as completing the series of basic rocks containing nepheline as an essential constituent.
• With a decrease in silica and reduction in olivine theralite grades into teschenite and with the addition of sodic feldspar, grades into essexite.
• Essexites are no longer considered part of the theralite group and are more properly known as " nepheline monzogabbro " or " nepheline monzodiorite ".
• We might in consequence regard them as varieties of syenite, diorite, gabbro, etc ., in which feldspathoid minerals occur, and indeed there are many transitions between syenites of ordinary type and nepheline  or leucite  syenite, and between gabbro or dolerite and theralite or essexite.