What labels like L6 and H5 mean

A label such as L6 or H5 packs two facts. The letters give the chemical group, here L or H ordinary chondrites, which differ in how much iron they hold. The digit is the petrologic type: 3 for the least altered rock, rising to 6 or 7 for rock strongly heated inside its parent asteroid. Among the 1,063 observed falls in NASA’s Meteorite Landings dataset (records to 2013), L6 alone covers 254 falls and H5 another 159.

The letters: chemical groups

Ordinary chondrites dominate the falls: 834 of 1,063, or 78 %. They come in three groups. H chondrites carry the most total iron and the most free metal, L chondrites less, and LL chondrites the least of both. A slash, as in L/LL6, marks a rock that sits between two groups. The record also has 32 falls labelled as intermediate, as plain “OC” or with a group letter but no type.

The other chondrite families are smaller. Carbonaceous chondrites, rich in carbon compounds and water-bearing minerals, number 44; their letters name a reference meteorite, so CM stands for the Mighei type and CI for the Ivuna type. Enstatite chondrites, EH and EL, number 17. The Rumuruti (R) and Kakangari (K) groups appear once each.

The digit: petrologic type

For ordinary chondrites the digit runs from 3 to 7. Type 3 rock still shows sharp chondrules, the small once-molten beads that give chondrites their name. Each step up means more heating on the parent body, which blurs the chondrules and evens out the mineral compositions. Type 6 is the most common in the falls: 386 of the 802 H, L and LL falls, against 38 of type 3.

The pattern differs by group. H falls cluster at type 5, L falls at type 6. Ranges such as H3-5 describe breccias, rocks made of fragments of several types, while a slash between digits, as in H4/5, means the type lies between the two. For carbonaceous chondrites the low digits mean something else: types 1 and 2 record alteration by water, so CI1 and CM2 rocks are the most water-altered of all.

Carbonaceous groups among the falls

CM is the largest carbonaceous group among the falls, with 15. The fall note on carbonaceous falls lists all 44 of them.

Achondrites, irons and stony-irons

Achondrites are stony meteorites whose parent body melted, so they lost their chondrules. The largest set among the falls is the HED group of 60: 33 eucrites, 16 howardites and 11 diogenites, rocks thought to come from one parent body. Their labels add texture words: “mmict” for a monomict breccia made of one rock type, “pmict” for a polymict breccia, “cm” for cumulate. Other achondrites number 19, led by aubrites. Five falls are Martian meteorites: Chassigny (1815), Shergotty (1865), Nakhla (1911), Zagami (1962), Tissint (2011).

Iron meteorites carry a chemical group made of Roman numerals and letters, such as IIIAB or IVA, defined by nickel and trace elements; 48 irons are falls. Stony-irons split into pallasites and mesosiderites, 11 falls in all. The iron falls note covers them in detail.

The ten most common labels

Three labels, L6, H5 and H6, cover 504 falls, 47 % of the record. The table lists the ten most common labels with their share and the median recovered mass of the falls that carry them. Medians sit between about two and five kilograms for all of them, which is why a single label says little about how large a particular fall was.

One of the ten, Stone-uncl, is not a real group at all; it marks stones without a classification. Another, Eucrite-mmict, is the only achondrite in the list. Everything else is an ordinary chondrite. Each label with twenty or more falls has its own page with a world map and a decade chart, linked from the table.

On this site each label is also placed in one of a dozen families, from L chondrites to irons, so that small labels can be compared with their relatives. The family names are plain descriptions, not official classes; the label itself always comes first, exactly as the record gives it.

The long tail is long: 61 of the 124 labels are carried by a single fall. Most of them are fine distinctions inside a big group, such as a decimal petrologic type (LL3.15, CO3.7) or an anomalous variant, rather than rare kinds of rock.

Leftovers and suffixes

“Stone-uncl” marks 23 stony falls that carry no group in the record; 15 of them fell before 1900. The suffix “-an” means anomalous: the rock fits its group in most respects but not all. Class labels on this site are shown exactly as in the record, with a plain-language line beside each one.

Does the class change the typical mass?

Somewhat. The median recovered mass differs by family, as the table shows, but every family spans grams to tonnes. A label describes the rock, not its size.

Every label in the record, with its count, is on the class index.