- Basanite
Basanite (pronEng|ˈbæsənaɪt) is an igneous, volcanic (
extrusive ) rock withaphanitic toporphyritic texture. Themineral assembly is usually abundantfeldspathoid s (nepheline orleucite ),plagioclase , andaugite , together witholivine and lesser iron-titanium oxides such asilmenite andmagnetite -ulvospinel ; minor alkalifeldspar may be present, as illustrated by the position of the field for basanite in theQAPF diagram .Clinopyroxene (augite ) andolivine are common asphenocryst s and in the matrix. The augite contains significantly greatertitanium ,aluminium andsodium than that in typical tholeiitic basalt.Quartz is absent, as areorthopyroxene andpigeonite . Chemically, basanites are low insilica (42 to 45% SiO2) and high inalkali s (3 to 5.5% Na2O and K2O) compared tobasalt , which typically contains more SiO2, as evident on the diagram used forTAS classification .Nephelinite is yet richer in Na2O plus K2O compared to SiO2.Basanites occur both on continents and on ocean islands. For example, together with basalts, they are produced by
hotspot volcanism in the Hawaiian and the Comores Islands. (e.g., [http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_65599.htm] )The term "basanite" has been used occasionally to refer to the mineral
jasper , for example a blackflint y or cherty jasper found in several New England states of the U. S. A. Such varieties of jasper are also informally known as Lydian stone, lydite andtouchstone and have been used to test for the purity ofprecious metal alloy s.References
*Blatt, Harvey and Robert J. Tracy (1996) "Petrology", 2nd ed., W. H. Freeman ISBN 0-7167-2438-3
* [http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_65599.htm Buchwaldt, Robert (2003) Geochemistry and Petrology of a Miocene Trachyte-Basanite Suite from Mt. Tsaratanana, Northern Madagascar, Abstract.]
* [http://www.mindat.org/min-9173.html Mindat data]
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