| 词条 | Howardite |
| 释义 |
|Subdivision = Group |Name = Howardite |Alternative_names = |Image = Howardite QUE94200.gif |Image_caption = QUE94200, a Howardite about {{Convert|5|cm}} across, found in the Queen Alexandra Range in Antarctica. |Image_alt_text = |Compositional_type = Stony |Type = Achondrite |Class = Asteroidal achondrite |Clan = HED meteorite |Structural_classification = |Parent_body = 4 Vesta |Composition = |Petrologic_type = |Number_of_specimens = ~200 |TKW = |Image2 = |Image2_caption = |Image2_alt_text = }}Howardites are achondritic stony meteorites that originate from the surface of the asteroid 4 Vesta, and as such are part of the HED meteorite clan.[1][2] There are about 200 distinct members known.[3] CharacteristicsThey are a regolith breccia consisting mostly of eucrite and diogenite fragments, although carbonaceous chondrules and impact melt can also occur. The rock formed from impact ejecta which was later buried by newer impacts and lithified due to the pressure from overlying layers. Regolith breccias are not found on Earth due to a lack of regolith on bodies which have an atmosphere. NameHowardites are named for Edward Howard, a pioneer of meteoritics. An arbitrary divide between howardites and the polymict eucrites is a 9:1 ratio of eucrite to diogenite fragments. See also
References1. ^Harry Y. McSween, Meteorites and their parent planets. Cambridge University Press, 1999. {{ISBN|0-521-58751-4}}, {{ISBN|978-0-521-58751-8}}. - [https://books.google.com/books?id=hFJ25RVuXfsC&pg=PA127&dq=Howardites#PPA129 p.129] 2. ^Howardite - daviddarling.info 3. ^Meteoritical Bulletin Database: Howardites External links
3 : Planetary science|Asteroidal achondrites|4 Vesta |
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