F , K , and R Type Chondrites  Guidelines
 

F Chondrites- Forsterite chondrites are intermediate in composition, mineralogy, and oxidation state between the H-group ordinary and enstatite chondrites. They represent a highly unequilibrated, distinct chondritic suite that underwent nebula condensation/accretion before the collision with the aubrite parent body. During brecciation, these highly shocked chondritic fragments were incorporated into the Cumberland Falls and ALH 78113 aubrites. So far, no independent, intact sample of this chondrite suite has been found.   

 

K Chondrites- The type specimen of this chondrite grouplet, Kakangari, along with two other members, have unique petrographic, bulk chemical, and O isotopic characteristics that distinguish it from other chondrite groups. The grouplet also does not fit into the existing systematics of the E, O, R, or C chondrites as their characteristics relate to heliocentric distance of formation. K chondrites therefore represent a unique, primitive, parent asteroid.
The unique petrologic and O-isotopic characteristics .
1. An oxidation state between H and E chondrites
2. A matrix unlike other chondrite groups (enstatite-rich and compositionally similar to the chondrules)
3. A high metal abundance similar to H group ordinary chondrites
4. Refractory lithophile and siderophile abundances similar to ordinary chondrites
5. Chalcophile elements that plot close to R chondrites whole-rock O isotopic compositions that plot near the CR chondrites
6. Chondrule O isotopic compositions that plot near the E chondrites  Chart below
 

R Chondrites- While this group of meteorites was initially distinguished through studies of the Carlisle Lakes, Australia specimen, its designation is now based on the only fall of the group from Rumuruti, Kenya. The group is highly oxidized, olivine-rich, and metal-poor. They differ greatly in oxidation state, oxygen isotope composition, and mineralogy from ordinary, carbonaceous, or enstatite chondrites, or silicate inclusions in IAB and IIE irons. The parent body was originally highly unequilibrated but was subsequently thermally metamorphosed and impact-melted to a moderate degree. Most R chondrites are highly brecciated and contain implanted solar wind gases, two features which are indicative of an origin from a surface regolith.

                              R Type Guidelines

R Type

Fa

Fs

Example
R 3-6

 1-60

1-30

NWA 2897
R 3

28

10

NWA 2446
R 4

38+ to 40

29.7

NWA 845
R 5

40+ to 41

30

NWA 830
R 6

38+ to 60 RC

 

La Paz 04840

 

 

 




RC is Relic Chondrules   These Fa and Fs are derived the the few known R types .

 

Modified Van Schmus-Wood Classification Scheme For R Chondrites
 

 R Type

3

4

5

6

Homogeneity
of olivine

>5% mean deviation

homogenous

homogenous

homogenous

Pyroxene

predominantly
low-Ca pyroxene

low-Ca and
Ca-rich pyroxene

only Ca-rich
pyroxene

only Ca-rich
pyroxene

Feldspar

small glassy
intergrowths

isolated intergrowths

networks forming

well-developed
networks

Sulfides

even distribution

even distribution

even distribution

mobilized

 


 

I/O Chart