Transitional Ordinary Chondrites

Besides several rare ungrouped and anomalous ordinary chondrites, such as the Fe-rich chondrites Burnwell and Willaroy which are considered members of a provisional HH grouplet (the "HH" standing for "high iron" and "high metal") by some, there are quite a few OCs that don't fit neatly into existing classification schemes, and that are often referred to as transitional ordinary chondrites. They are either classified as H/L chondrites or as L/LL chondrites, indicating that they share features of two established OC groups. They will be discussed below.

Transitional H/L Chondrites: The H/L members share features of both, H and L group chondrites. They're not to be confused with weathered desert finds that are sometimes classified as H(L) by scientists, indicating that the weathering grade makes it hard to distinguish if we are looking at a genuine H or at an L type. If we exclude these questionable cases of weathered desert finds, the Meteoritical Bulletin Database lists just about 25 genuine H/L members, incl. three witnessed falls: Bremervörde, Sharps, and Tieschitz.

It's not yet clear if the H/L chondrites do originate from a yet unidentified, separate OC parent body, or if they are anomalous representatives of either the L or the H chondrite parent body. The fact that, e.g., the H/L3.6 Tieschitz is a regolith breccia might be an indicator for the latter case. Tieschitz also contains pre-solar grains that obviously originated in red giant stars, and even some grains with a compostion consistent with an origin from a type II supernova.

Transitional L/LL Chondrites: The L/LL members have features of both, L and LL group chondrites, and as for the genuine H/L members it is important not to confuse them with L(LL) or LL(L) classifications which denote an uncertainty by the classifying scientist when it comes to the identification of weathered desert finds. If we subtract all these questionable cases, the Meteoritical Bulletin Database lists just 65 genuine L/LL chondrites, incl. nine witnessed falls: Albareto, Bjurböle, Cabezo de Mayo, Cynthiana, Glanerbrug, Knyahinya, and Trysil. 

There is some evidence that the L/LL members actually constitute an individual, third low-total-iron OC group from a distinct parent body. More recent research has shown that bulk REE contents in L/LL chondrites seem enriched relative to the L and LL group chondrites, and apparently all L/LL members exhibit a negative europium anomaly. Besides that, the olivine compositions of L/LL members are rather typical, as is the cobalt content in  matrix kamacite. The separate L/LL parent body could be an S-type asteroid, such as 69230 Hermes, a binary Apollo-type near-Earth asteroid with spectral properties consistent with L/LL chondrites.