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95:) and the concomitant reduction in nepheline, theralite becomes gabbro. With a decrease in silica and reduction in olivine theralite grades into teschenite and with the addition of sodic feldspar, grades into essexite. With a further reduction in silica such that there is no feldspar these rocks become melteigites. With the addition of alkali feldspar replacing or becoming more dominant than calcic plagioclase theralites grade into foidal syenite, including
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Teschenites were once considered part of the theralite group. They contain essential pyroxene, olivine and analcime rather than nepheline. Modern petrology would classify the teschenites as an analcime-bearing gabbro. They are petrogenetically unrelated to nepheline gabbros as analcime is not
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is a form of silica-undersaturated pyroxene gabbro, containing nepheline and orthoclase as essential constituents, though often in small proportions. Essexites can be considered to represent the intrusive equivalent of an alkaline basalt.
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Properly theralite is only for a specific type of calcic foidal gabbro, those with essential nepheline and without essential analcime or sodic feldspar.
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is foidal basalt with essential calic plagioclase but without essential olivine. It is essentially the volcanic equivalent of
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Essexites are no longer considered part of the theralite group and are more properly known as
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Essexites are usually associated with other alkaline, silica undersaturated to
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284:. Vol. 26 (11th ed.). Cambridge University Press. pp. 791–792.
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in these rocks may be of green colour or purplish-brown and rich in
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This article incorporates text from a publication now in the
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with essential calic plagioclase and essential olivine.
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This contains more detailed analytic and location data.
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72:Theralite is the intrusive equivalent of nepheline
138:intrusive rocks and coeval high-alumina basalts.
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207:Learn how and when to remove this message
170:This article includes a list of general
119:produced by the same genetic processes.
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91:With the increase in silica (SiO
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22:(from Greek "to pursue") is, in
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26:, the name given to calcic
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378:Igneous petrology stubs
281:Encyclopædia Britannica
191:more precise citations.
147:nepheline monzodiorite
143:nepheline monzogabbro
313:This article about
373:Igneous petrology
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315:igneous petrology
268:Flett, John Smith
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16:Igneous rock
189:introducing
114:Teschenites
76:, a foidal
47:labradorite
43:plagioclase
362:Categories
243:Flett 1911
231:Flett 1911
172:references
153:References
136:monzonitic
97:shonkinite
41:, calcic
272:Theralite
270:(1911). "
123:Essexites
59:magnetite
51:nepheline
24:petrology
20:Theralite
128:Essexite
105:titanium
101:Pyroxene
86:essexite
82:Tephrite
74:basanite
67:analcime
63:ilmenite
278:(ed.).
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185:improve
55:biotite
49:), and
39:olivine
274:". In
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78:basalt
35:augite
31:gabbro
28:foidal
317:is a
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65:and
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