Acapulcoites Chart
Acapulcoites have average grain sizes of 150 to 230μm with Rare relict chondrules .
Rare but easily seen grains of chrome-diopside are found in Acapulcoites and Lodranites .
Metal FeNi 5 to 14 %
Triolite 3 to 6 %
Olivine Fo95.8 20 to 30%
Orthopyroxene En93.5-87.4 40% (Ca-poor pryoxene )
Plagioclase An15 to 12
Ca-pyroxene Cr-diopside
Kamacite is ubiquitous in all but the most reduced specimens with olivine Fo95.8
Oxygen Isotopic tests
Acapulcoites and Lodranites share many similarites including I/O but
as you can see grain size is quit different !
Acapulcoites were heated above the Fe,Ni-FeS eutectic
But below the silicate solidus
Brachinites Chart
Brachinites have an average grain size of 200 to 1000μm but with NO relict chondrules !
Olivine Fo65-70
Orthopyroxene En74-72 (Ca-poor pryoxene ) ONLY TRACE AMOUNTS !!
Ca-pyroxene Cr-augite
Metal FeNi ONLY TRACE AMOUNTS and the Ni portion 19-55 wt%
Note the sample of Eagles Nest a 1.2g fragment is slightly magnetic !
Brachinites have a granular fabric dominated by olivine grains that meet in triple junctions
which rarely may be prismatic and display preferred orientation .
Oxygen Isotopic tests
Lodranites Chart
Lodranites have an average grain size of 340 to 700μm but with NO relict chondrules !
Rare but easily seen grains of chrome-diopside are found in Acapulcoites and Lodranites .
Metal FeNi 0.2 to 20 %
Triolite 0.1 to 5.3%
Olivine Fo97-87 83 to 30%
Orthopyroxene En96-86 6 to 50% (Ca-poor pryoxene )
Plagioclase An31-15
Ca-pyroxene Cr-diopside
Oxygen Isotopic tests
Acapulcoites and Lodranites share many similarites including I/O but
as you can see grain size is quit different !
Lodranites were more strongly heated than Acapulcoites .
Some were heated above the silicate solidus 1150 C causing fractionation of
the ( plagioclase-Ca-Pyroxene ) liquid .
The metal appears "lumpy" at times .
Winonaties Chart
Winonaties have an average grain size of 55-230 < 1000 but with rare recrystallized relict chondrules !
Metal FeNi 0.1 to 12.5 %
Triolite 1 to 19%
Graphite 0 to 0.6%
Schreibersite 0 to 1%
Olivine Fo100-95 15 to 30%
Orthopyroxene En100-91 25 to 45% (Ca-poor pryoxene )
Plagioclase An25-7
Ca-pyroxene Cr-diopside
Graphite may rim inclusions or individual grain .
Winonaties are shock stage S1 yet the olivines and pyroxenes may be recrystallized .
Primitive achondrites are those meteorites whose bulk compositions are approximately chondritic, but have been texturally modified by partial melting or metamorphic recrystallization. Because primitive achondrites are very different from other meteorites, but have similarities within themselves, they will be discussed here as a diverse group. A fundamental distinction between the acapulcoite and lodranite classes is that lodranites are relatively coarse-grained (0.5 to 1.0 mm) and acapulcoites are finer-grained (0.2 to 0.4). However, they are not easily distinguishable on casual observation; nor are they distinguishable using oxygen isotopes (figure below).
