HED Meteorite  Guidelines
Eucrites
Diogenites

Howardites    Chart   O/I chart
 
Howardites are polymict breccias composed of angular clasts of eucrites and diogenites mixed together in a crushed matrix .
 They do not have unique mineral characteristics like other meteorite classes
But one defining parameter is that the composition mean average must contain more than 10% Diogenitic material .

Monomict Goup
The monomict subgroup containing eucrites, cumulate eucrites, and diogenites is further subdivided .
A brecciated
B unbrecciated

Polymict Group
The polymict subgroup samples a compositional and textural continuum of regolith and surface breccias
consisting of eucrites, cumulate eucrites, diogenites, and howardites.
Those meteorites containing more than 90% of a single component are given the prefix "polymict"
attached to their present description

   
Polymict eucrites contain less than 10% non-eucritic material; polymict diogenites contain more
than 90% orthopyroxenite or hypersthene). Those meteorites that contain less than 90% of any single
component are defined as howardites. While this 10% level is still an arbitrary dividing line based simply
on mineral proportions, it represents an amount of orthopyroxene that can easily be detected by X-ray
diffraction techniques. An additional tool to distinguish between polymict eucrites and howardites involves
pyroxenes in the basaltic clasts; within howardites they are mostly unzoned whereas in polymict eucrites
they are usually zoned.

 

Classic modern write up
Northwest Africa 1929
Morocco
Find:  May 2003
Achondrite (howardite)

History:
A 922.2 g partially crusted, complete stone was purchased in Erfoud, Morocco in 2003 May. Petrography: (T. Bunch and J. Wittke, NAU) A breccia of 72 vol. % cumulate eucrite clasts, 8% subophitic clasts, 14% diogenites and 6% melt clasts. Pervasive solid-state recrystallization of plagioclase and pyroxenes with localized melt pockets and veins in clasts. Geochemistry: Coarse-grained gabbroic eucrite pyroxene, Fs45-40Wo7-20; plagioclase, An91.2-95.3; Metal inclusions Ni = 0.97; Cr = 0.87 (both wt %); Diogenite pyroxene, Fs43-54Wo2.5-3.6. Classification:  Achondrite (howardite), heavily shocked.  Specimens: A 22.02 g specimen is on deposit at NAU. Farmer holds the main mass.
 

Northwest Africa 2060
Morocco
Found 2003
Achondrite (howardite)

A 985 g, very fresh stone with shiny fusion crust, was purchased in Rissani, July 2003. Classification and mineralogy (T. Bunch and J. Wittke, NAU): a howardite of unusual characteristics. Fine-grained and powdery, average clast and mineral grain size is < 2 mm with few clasts > 3 mm. Clast modes: diogenites, 74 vol. %; eucrites 20 vol. % (12 % cumulate, 8 % basaltic); anorthositic-like clasts, 3 %; shock melt clasts. 2 %, and opaques, 1%. Diogenite orthopyroxene, Fs35.6-38.8Wo2.3-4.2; plagioclase, An 87; chromite, Cr/(Cr+Al) = 0.81; metal, Ni = 0.67 wt %. Melt inclusions in opx contain Ca-rich pyroxene, Fs33.3Wo37.5; phosphate, silica phase, and K-rich glass. Plagioclase-pyroxene cumulates, Fs38.2Wo21; plagioclase, An86.Other eucrite textures include recrystallized, granular, ophitic, subophitic, and variolitic (Fs31.6Wo7 and Fs61.8Wo33). Plagioclase-rich clasts have 95 vol.% plagioclase (An96.1). Mildly shocked; no apparent oxidation or Fe staining. Specimens: 26 g, NAU: main mass. Boswell.
 

Eucurites  Chart   O/I chart
 
Eucrites are composed of orthopyroxene, pigeonite, Ca-rich pyroxenes and plagioclase with minor amounts of chromite, ilmenite, troilite and Ni-Fe metal. A few eucrites, such as  Moore County are similar to terrestrial gabbros (plutonic rocks) in having cumulate textures (preferred orientation of major minerals) that indicate crystal layering by settling-out in a magma chamber, analogous to the accumulation of fallen tree leaves into layered piles.
But one defining parameter is that the composition mean average must contain Less than 10% Diogenitic material .
 

The members of the achondrite classification can be placed into two specific subgroups:
 

  1. Primitive - igneous-textured meteorites that are nearly chondritic in bulk composition and retain geochemical and isotopic characteristics of their precursors (lodranites, acapulcoites, winonaites, IAB silicates, brachinites, and ureilites)
     
  2. Evolved - the above primitive characteristics have become obliterated due to more extensive igneous processing (HEDs, SNCs, lunaites)

The eucrites of the evolved subgroup have been petrographically divided into a metamorphic sequence comprising six types (after Takeda and Graham, 1991):
 

  1. Type 1 - most quickly cooled in the sequence; mesostasis-rich with glass phase and original chemistry preserved; exhibit pronounced Mg-Fe zoning in pyroxenes; represent the least altered basalt studied
     
  2. Type 2 - metastable Fe-rich pyroxenes are absent; mesostasis glass is no longer clear
     
  3. Type 3 - zoning from core to rim is less defined with an increase in Ca towards the rim; pyroxenes becoming cloudy; coarsening of pyroxenes resulting from augite exsolution lamellae
     
  4. Type 4 - only remnants of zoning still visible; cloudy pyroxenes present; mesostasis glass is recrystallized or absent; augite exsolution lamellae becoming resolvable in microprobe
     
  5. Type 5 - homogenous host composition with readily resolvable exsolved pigeonite lamellae; pigeonites extensively clouded by reheating; mesostasis glass recrystallized or absent
     
  6. Type 6 - most slowly cooled eucrites in the sequence; the clinopyroxene pigeonite is partly inverted to orthopyroxene through slow cooling processes; pyroxenes contain Mg-rich cores and coarse augite exsolution lamellae; original mesostasis is absent; Ca is enriched in the rims; often have a brecciated texture

    Eucrites Groups

    1. Cumulate Group   Example Dhofar 007

    2. Noncumulate / Monomict Group 

    Main group 
    Example Camel Donga

    Stannern Trend
      Example Stannern

    Nuevo Laredo Trend  Example Igdi

    3. Polymict Group  Example  Smara

    The polymict subgroup samples a compositional and textural continuum of regolith and surface breccias
    consisting of eucrites, cumulate eucrites, diogenites, and howardites.
    Those meteorites containing more than 90% of a single component are given the prefix "polymict"
    attached to their present description

       
    Polymict eucrites contain less than 10% non-eucritic material; polymict diogenites contain more
    than 90% orthopyroxenite or hypersthene). Those meteorites that contain less than 90% of any single
    component are defined as howardites. While this 10% level is still an arbitrary dividing line based simply
    on mineral proportions, it represents an amount of orthopyroxene that can easily be detected by X-ray
    diffraction techniques. An additional tool to distinguish between polymict eucrites and howardites involves
    pyroxenes in the basaltic clasts; within howardites they are mostly unzoned whereas in polymict eucrites
    they are usually zoned.



     

Classic Modern write up

Northwest Africa 1836
Morocco
Found 2002
Achondrite (monomict eucrite)

A 1102 g partially crusted, single stone was purchased in Rissani, Morocco in 2003. Classification and mineralogy (T. Bunch and J. Wittke, NAU): highly contorted mass of eucrite clasts with cataclastic mantles that are in turn covered by partially melted to recrystallized masses. Cumulate texture with subophitic enclaves. Clast orthopyroxene, Fs56.4–59Wo2.5–4; exsolution lamellae, Fs43.4-46.3Wo23-25.6; recrystallized zone, Fs54.5–57.5Wo8.4–13.5. Chromite, Cr/(Cr+Al) = 0.85, TiO2 = 14.6 wt. % with exsolution lamellae of ilmenite; plagioclase, An91–93.6. Shock level, S1 to S5. The meteorite is very fresh. Specimens, 25.5 g, NAU; main mass, Oakes.
 

Orlando                                 28° 32' 51²N 81° 21' 44²W
Orange County, Florida, U. S. A.
Fell 2004 November 8
Achondrite (eucrite)

History: On Monday, November 8, 2004, around 6:15 p.m., Ms Donna Shuford was startled by the noise of something hitting the side of her house. She discovered that something had hit the top of her car and ricocheted onto the side of her house. A single stone, mass ~180 g, had fragmented on impact. Petrography and Geochemistry: (D. Mittlefehldt and M. Zolensky, NASA JSC) Major phases are low-Ca pyroxene, Wo3En35Fs62, Fe/Mn ~30 with lamellae of high-Ca pyroxene Wo45En29Fs26 and calcic plagioclase An71-83Ab16-28Or~1. Minor phases include titanian chromite (TiO2 = 16-20; Al2O3 = 2-3; MgO = 0.4; MnO = 0.8; all wt%); Ilmenite (MgO = 0.5; MnO = 0.9 (both wt%); with silica, iron sulfide, and Fe-Ni metal.  The rock is largely unbrecciated, but has shock veins with granular texture and containing some glass.  Remnant ophitic/sub-ophitic igneous texture is preserved with plagioclase laths ~1 mm by ~30 µm, and ~2 mm blocky pyroxene grains.  In much of the rock pyroxene has been recrystallized to ~20-50 µm equant grains while plagioclase retains its original shape.  Classification: Achondrite (monomict basaltic eucrite).  Specimens: A 20 g specimen on deposit at SI. The finder holds the main mass.


 


Diogenites  Chart   O/I chart
 
Diogenites  are composed essentially of orthopyroxene and hypersthene, with minor amounts of plagioclase, olivine, troilite, and chromite. 
Like eucrites, diogenites contain little NiFe metal , most diogenites have been crushed to some degrees. 
 The remaining hypersthene crystal fragments are as large as 6 cm .
With the extreme severity of crushed: individual crystals it is not readily identified unless viewed in crossed-polarized light.
In this light component fragments show some rotation and small pockets of crushed  material.

Diogenite Groups
1. Monomict Diogenite Group  Example  Johnstown

2. Polymict diogenite Group     Example  NWA 1239

3. Olivine Diogenite Group       Example  NWA 2115

Polymict Group
The polymict subgroup samples a compositional and textural continuum of regolith and surface breccias
consisting of eucrites, cumulate eucrites, diogenites, and howardites.
Those meteorites containing more than 90% of a single component are given the prefix "polymict"
attached to their present description

   
Polymict eucrites contain less than 10% non-eucritic material; polymict diogenites contain more
than 90% orthopyroxenite or hypersthene). Those meteorites that contain less than 90% of any single
component are defined as howardites. While this 10% level is still an arbitrary dividing line based simply
on mineral proportions, it represents an amount of orthopyroxene that can easily be detected by X-ray
diffraction techniques. An additional tool to distinguish between polymict eucrites and howardites involves
pyroxenes in the basaltic clasts; within howardites they are mostly unzoned whereas in polymict eucrites
they are usually zoned.

 


Classic write up
 

Northwest Africa 1648
Morocco
Purchased 2002 October
Achondrite (diogenite, polymict)

A complete fusion-crusted stone (803 g) was purchased from a Moroccan dealer by A. and G. Hupé (Hupé). Classification and mineralogy (A. Irving and S. Kuehner, UWS): Heterogeneous breccia composed of multiple clast types of varying size. Angular mineral clasts are predominantly orthopyroxene with subordinate anorthite (Ab5), silica, exsolved pigeonite, ilmenite and troilite. The orthopyroxene clasts are homogeneous and have low Ca contents, but range widely in Fe/Mg ratio (FeO = 12.6–22.5 wt%, FeO/MnO = 28.2–34.8), suggesting multiple diogenitic parent rocks. Sparse polycrystalline clasts include cumulate eucrites, basaltic eucrites, a quench-textured clast consisting of dendritic olivine grains in glass, and fine grained ferroan inter-growths (breakdown of former pyroxferroite) composed of hedenbergite + fayalite + silica ± ilmenite ± troilite attached to anorthite laths. Breccia consisting of various diogenites (>80% by volume), sparse cumulate eucrites and rare basaltic eucrites. Specimens: type specimen, 22 g, and thin section, UWS; main mass, Hupé.

 

Northwest Africa 1877
Morocco
Purchased 2003 June
Achondrite (Olivine-rich diogenite)

A partly crusted stony meteorite (312 g) was purchased in Zagora by a Moroccan dealer for A. and G. Hupé (Hupé) in 2003 June and more of the same material (622 g) was purchased in Tagounite in 2003 December. Classification and mineralogy (A. Irving and S. Kuehner, UWS): Coarse grained, dense and somewhat friable, with an overall yellow-green color.  Harzburgitic peridotite composed of subequal amounts of orthopyroxene (Fs22.4-23.3Wo1.5; FeO/MnO = 25.2-29.7) and olivine (Fa27.8, FeO/MnO = 44-50) with minor Al-poor chromite [Cr/(Cr+Al) = 84.8-88.0, Mg/(Mg+Fe) = 11.7-19.8], troilite (as abundant blebs within silicates and as inclusions in chromite), and sparse Ni-free metal (partly altered to limonite).  The modal amount of olivine estimated from three serial thin sections is approximately 45%, which is consistent with the moderately high density of this meteorite. The relatively magnesian silicate compositions are similar to those in Antarctic olivine diogenite GRA98108, and quite different from those in another Moroccan olivine diogenite NWA 1459 (Irving et al., 2003).  Unlike both of these examples, however, NWA 1877 does not contain plagioclase.  Specimens: type specimen, 24 g and three polished thin sections, UWS; main mass, Hupé.

 

Northwest Africa 2434
Northwest Africa
Purchased 2004
Achondrite (diogenite, metal-rich)

A 441 g partially crusted stone was purchased in Erfoud, Morocco. Description and classification (J. Wittke and T. Bunch, NAU): highly brecciated, metal-rich diogenite with orthopyroxene fragments up to 11 mm in size and scattered recrystallized pockets. Modal content in vol. %: orthopyroxene, 86.2; metal, 7.3 (heterogeneously distributed, 4.3 to 13.2 vol. %); plagioclase, 5.5, phosphate, sulfide and chromite < 2. Orthopyroxene, Fs24.2Wo1.3 (FeO/MnO = 32.7); Ca-rich pyroxene, Fs8Wo46.9; plagioclase, An95.7; chromite, cr# = 69; metal, Ni = 6.5 wt. %. Very fresh; shock level, S2. Specimens: type specimen, 27.6 g, NAU; main mass, Hall.


 

The following sections present specimen illustrations and descriptions of differentiated achondrites, which includes the HED clan (howardites, eucrites, and diogenites), angrites, aubrites, and ureilites. A summary of the diagnostic mineralogic characteristics of all achondrites is given in the table below (modified after Table 8.1 in Hutchison, 2004, Meteorites: A Petrologic, Chemical and Isotopic Synthesis, Cambridge University Press).

 Differentiated
 Achondrites
Acapulcoite & Lodranite 1AB iron silicate & Winonaite  Ureilite Brachinite Aubrite Eucrite Diogenite Howardite Angrite
Olivine/Pyroxene <=1 <1 >1 >>1 <<1 <<1 <<1 <<1 1
Olivine Fa3-14 Fa1-8 Fa5-25 Fa30-35 Fa0 - Fa27-35 Fa8-89 Fa10-100
Olivine Fe/Mn                  
Orthopyroxene En86-97 En91-99 En80-90 tr En100 tr En67-77 variable -
Ca-pyroxene En51Wo44  min En75Wo15  min En50Wo50 variable tr variable Wo>50
Plagioclase An12-31 An8-25 - An22-32 tr: An2-8 An60-98 An60-91 An60-98 An100
Silica - - - - - tr tr tr -
Kamacite  min  min  min -  min tr-min tr tr tr
Taenite  min  min - tr tr - - tr -
Troilite  min  min tr  min tr tr tr tr tr

Notes:  min = minor, <5 vol. %; tr = trace, <0.5 vol. %

 
O/I