Textural Types of Meteorites

1. Orbits determined from observed meteorite falls indicate that most meteorites originate from the asteroid belt. Several additional orbits have been determined since this diagram was drawn, all of which support this origin.

2. Textural Types of Meteorites Stony meteorites Chondrites – contain chondrules Achondrites – textures of igneous rocks Iron meteorites Hexahedrites (H) – consist of kamacite without taenite. Low Ni-content. Octahedrites (O) – consist of kamacite lamellae with remnant taenite . Ataxites (D) – consist of taenite only. High Ni-content. Stony-iron meteorites Mesosiderites – mixed silicates and iron Pallasites – olivines in a kamacite matrix

3. Chondrites Chondrites are believed to have formed in the condensation of the solar nebula. Hence, they were never molten, but have been subjected to various intensities of recrystallization, characterized by grades from 1 to 6. Enstatite chondrites (E) EH are grades 3 and 4. EL are grades 5 and 6. H and L refer to high and low iron. EH and EL are generally believed to have separate origins.

4. Abee (EH4) Fell June 9, 1953, at Abee, Alberta

5. Ordinary Chondrites • H – Olivine-Bronzite • L – Olivine-Hypersthene • LL – Amphoterites (Olivine-Pigeonite)

6. Bruderheim (L6) Fell on March 4, 1960, at Bruderheim, Alberta

7. Chondrule from Riverton [Manitoba], an H5 ordinary chondrite

8. Carbonaceous chondrites (C) – These represent some of the most primitive matter in the solar system. The Canadian meteorite, Tagish Lake, which fell in January, 2000, is a C2, probably the most primitive material ever recovered. The C-chondrites are subdivided according to chemical and petrographic characteristics into CI, CM, CH, CO, CV and CV. CI chondrites do actually contain chondrules but on the basis of their chemistry are considered to be C-chondrites. The C-chondrites have grades 1, 2 and 3, but grades 1 and 2 reflect degrees of aqueous alteration and grade 3 is essentially unaltered.

9. Achondrites • Aubrites • Diogenites • Ureilites • Angrites • Lorandites • Howardites • Eucrites SNC meteorites – Martian meteorites Shergottyites Nakhlites Chassignites

10. Stannern (Eucrite) Fell at Stannern, Bohemia (now Czech Republic) in 1908.

11. SNC (Martian) Meteorites • ALH84001 (Allan Hills, Antarctica). This is the famous (or infamous) carrier of purported fossil life on Mars. Not actually an SNC type.

12. Detail of Allende, showing CAI inclusion (calcium-aluminum inclusion), believed to represent condensation from the solar nebula.

13. Stony Irons • Giroux (Pallasite) found at Giroux, Manitoba

14. Detail of Springwater Pallasite, found near Springwater, Saskatchewan.

15. Esterville (Mesosiderite) Found at Esterville, Iowa

16. Iron Meteorites Iron meteorites were originally classified entirely on their textures. Octahedrites can also be further classified based on the width of their kamacite lamellae: Coarsest (Ogg) > 3.3 mm Coarse (Og) 1.3 – 3.3 mm Medium (Om) 0.5 – 1.3 mm Fine (Of) 0.2 – 0.5 mm Finest (Off) < 0.2 mm Plessitic Octahedrites (Opl) <0.2 mm spindles

17. The kamacite bandwidth is directly related to the Ni-content. As well, the principal trace and minor elements Ni, Ge, Ga and Ir lead to a chemical classification of iron meteorites. In addition As, Co, Cu, P, Pt, Re, Sb, and W have taxonomic value. These factors yield 13 chemical groups: All of the iron meteorites were originally molten; i.e. magmatic in the true sense. However, they are classed as magmatic and non-magmatic on another basis. Non-magmatic groups – do not display magmatic trace element fractionation trends. IAB IIICD These two groups are now considered to be one called IAB Complex.

18. Magmatic groups – display magmatic fractionation trends IC IIAB IIC IID IIE IIF IIIAB IIIE IIIF IVA IVB

19. Henbury (Om group IIIAB) This polished and etched slice displays the Widmanstaetten pattern, characteristic of octahedrites.