Hawaiite is anolivinebasalt with a composition betweenalkali basalt andmugearite.[1] It was first used as a name for some lavas found on the island ofHawaii.
It occurs during the later stages of volcanic activity on oceanic islands such as Hawaii,[2] which happens to be when the alkali metals are most present.[3]
Ingemology, hawaiite is acolloquial term for Hawaii-originatedperidot, which is agem-quality form of the mineralolivine.[4]
Hawaiite is anaphanitic (fine-grained)volcanic rock produced by rapid cooling oflava moderately poor insilica and enriched inalkali metal oxides (potassium oxide plussodium oxide). It is often impractical to determine themineral composition of such a fine-grained rock, and so hawaiite is defined chemically. Under theTAS classification, hawaiite is sodictrachybasalt, with a silica content close to 49 wt%, a total alkali metal oxide content close to 6%, andNa2O wt% >K2O wt% + 2. This places hawaiite in the S1 field of the TAS diagram.[5][6]
Hawaiite is not a recognized rock type in theQAPF classification ofigneous rock, which is based on the relative proportions ofquartz,alkali feldspar, andplagioclase in the mineral composition. However, hawaiite is composed mostly ofandesine (plagioclase feldspar with analbite content of 50% to 70%) andpyroxene with smaller amounts ofolivine.[1] This would fall into theandesite/basalt field of the QAPF diagram.[7]
Hawaiite is erupted in the late stages of ocean island volcanism, forming part of thealkaline magma series characteristic of such eruptions. It is preceded by silica-poorankaramite and followed by intermediate-silicamugearite as themagma evolves by crystallization in the underlyingmagma chamber. These rocks form analkalic cap over the older rocks of the island.[8] Hawaiite can occur at earlier stages in the evolution of some volcanoes in other tectonic settings, for example during the middle stage of volcanic activity in the Kekuknai volcanic massif (inKamchatka, Russia) that formed in a volcanicback-arc basin.[9]
Other settings in which hawaiite and other alkaline volcanic rocks are found include regions of continental extension, such as theBasin and Range Province of western North America[10] and theRed Sea Rift.[11]
Types ofbasalts | |
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| Basalts by tectonic setting | |
| Basalts by form and flow | |
| Basalts by chemistry | |
| Important minerals | |
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