Alkali basalt
A rock classification type
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About Alkali basalt
A term used for a basaltic rock containing accessory foids, typically nepheline. Such rocks generally contain calcic plagioclase, augite and olivine as their main phases. Defined as a variety of basalt within TAS field B which contains normative nepheline, or as the equivalent foids-bearing basalt in field 10’ in the QAPF diagram. With increasing silica it grades into tholeiitic basalt, and with decreasing silica into basanite or tephrite.
Unique Identifiers
Mindat ID:
48493
Long-form identifier:
mindat:1:1:48493:4
GUID
(UUID V4):
(UUID V4):
4b946483-c602-4ea1-bbcc-cc0a77ec3f25
Classification of Alkali basalt
Alkali basalt appears in field 10' in the QAPF diagram.
Alkali basalt is found in field B in the TAS diagram.
Sub-divisions of Alkali basalt
- Alkali basalt
Mineralogy of Alkali basalt
Essential minerals - these are minerals that are required within the classification of this rock:
Calcic plagioclase | A petrological term for plagioclase series feldspars dominant in calcium. |
Feldspathoid | A family of rock-forming minerals consisting of aluminosilicates of sodium, potassium, or calcium and having too ... |
Feldspathoid > Nepheline | Na3K(Al4Si4O16) |
Olivine | Commonly used as a synonym for a member of the Fayalite-Forsterite Series, but more generally and properly ... |
Titanium-bearing Augite | (Ca,Na)(Mg,Ti, Fe,Al,)(Si,Al)2O6 |
Age distribution
Recorded ages:
Phanerozoic : 67.7 ± 0.7 Ma to 0.212 ± 0.038 Ma - based on 7 recorded ages.
Synonyms of Alkali basalt
Common Associates
Associated Minerals Based on Photo Data:
2 photos of Alkali basalt associated with Augite | (CaxMgyFez)(Mgy1Fez1)Si2O6 |
2 photos of Alkali basalt associated with Bomb-tephra |
Internet Links for Alkali basalt
mindat.org URL:
https://www.mindat.org/min-48493.html
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References for Alkali basalt
Reference List:
Lake Turkana, Marsabit County, Kenya