Alkali basalt

[3] Alkali basalt is characterized by relatively high alkali (Na2O and K2O) content relative to other basalts and by the presence of olivine and titanium-rich augite in its groundmass and phenocrysts, and nepheline in its CIPW norm.

[6] The groundmass of alkali basalt is mainly composed of olivine, titanium-rich augite and plagioclase feldspar and may have alkali feldspar or feldspathoid interstitially, but is poor in silica minerals, such as hypersthene and quartz.

[4] Phenocrysts are ubiquitous in alkali basalt and, similarly to the groundmass, are usually made up of olivine and titanium-rich augite but can also have plagioclase and iron oxides with lower frequency.

[3][4] Alkali basalt can be found in areas associated with volcanic activity, such as oceanic islands (Hawaii, Madeira,[7] Saint Helena,[8] Ascension, etc.

[9] The results from the gamma ray spectrometer on Venera 8 on Venus suggest it landed on alkali basalt.