Basalt
unit |
Core, section, piece,
interval (cm) |
Size
(µm) |
Titanomagnetite description
|
Estimated
modal abundance (%) |
Other opaque minerals
|
Photomicrograph
|
|---|---|---|---|---|---|---|
| 197-1206A- | ||||||
| 1 | 3R-2 (Piece 8, 94-96) |  80 |
Skeletal octahedra and dendrites; ilmenite oxidation lamellae are well developed and maghemite is developed along cleavage planes | 6-8 | Cr spinel inclusions are present in altered olivine phenocrysts; these usually have a titanomagnetite overgrowth, but occasionally are unaltered; no sulfide or Fe oxyhydroxide | 1206A-289, 1206A-290, 1206A-291, 1206A-292 |
| 1 | 4R-3 (Piece 4A, 72-74) | 100 |
Skeletal octahedra and dendrites (up to 200 µm); slight development of ilmenite oxidation lamellae, but no maghemite | 6-8 | Cr spinel inclusions are present in olivine; these usually have a titanomagnetite overgrowth, but occasionally are unaltered; no sulfide or Fe oxyhydroxide | 1206A-293, 1206A-294, 1206A-295, 1206A-296, 1206A-297, 303, 1206A-304 |
| 2c | 7R-1 (Piece 9, 123-125) | — | Lobe margin; no titanomagnetite is present | — | Cr spinel inclusions in olivine phenocrysts; glass is now altered to a black-brown amorphous clay; no sulfide or Fe oxyhydroxide | |
| 4 | 8R-1 (Piece 1, 2-3) | 30 |
Skeletal octahedra and dendrites; extensive alteration to maghemite; rare titanomagnetite relicts are present parallel to cleavage planes | 2-4 | Cr spinel inclusions are present in altered olivine phenocrysts; Fe oxyhydroxide is present; no sulfide | |
| 4 | 8R-1 (Piece 24, 99-101) | 30 |
Skeletal octahedra and dendrites; extensive development of ilmenite oxidation lamellae and alteration to maghemite along cleavage planes and fractures; rare titanomagnetite relicts are present parallel to cleavage planes | 2-4 | Cr spinel inclusions are present in altered olivine phenocrysts; Fe oxyhydroxide is pervasive; no sulfide | |
| 4 | 8R-2 (Piece 1, 2-3) | 30 |
Skeletal octahedra and dendrites; extensive alteration to maghemite; rare titanomagnetite relicts are present parallel to cleavage planes | 2-4 | Cr spinel inclusions are present in altered olivine phenocrysts; Fe oxyhydroxide is present; no sulfide | |
| 5 | 15R-1 (Piece 7A, 72-74) | 50 |
Skeletal octahedra; mostly unaltered, but there is some development of ilmenite oxidation lamellae; maghemite is rarely present along fractures | 7-9 | Cr spinel is present with extensive titanomagnetite overgrowths (e.g., photomicrograph 1206A-323), but not distinguished as inclusions in olivine; no sulfide or Fe oxyhydroxide | 1206A-323, 1206A-324 |
| 5 | 15R-3 (Piece 15, 87-89) | 70 |
Skeletal octahedra; titanomagnetite is altered to maghemite along cleavage planes and fractures; ilmenite oxidation lamellae are present in unaltered titanomagnetite | 5-7 | Chromite inclusions are present in clinopyroxene and plagioclase crystals that form glomerocrysts; Fe oxyhydroxide is present in altered olivine phenocrysts; no sulfide | 1206A-322, 1206A-325, 1206A-326, 1206A-327 |
| 6 | 16R-4 (Piece 8B, 80-82) | 60 |
Anhedral, skeletal dendrites; ilmenite oxidation lamellae are probably present and the titanomagnetite may be partially altered to maghemite; small size and skeletal form makes positive identification difficult | 4-6 | Cr spinel inclusions are present in altered olivine phenocrysts; most Cr spinel inclusions have been replaced by titanomagnetite; olivine is replaced by Fe oxyhydroxide (iddingsite); no sulfide | 1206A-1206A-368, 369, 1206A-370 |
| 6 | 16R-5 (Piece 8, 66-67) | 20 |
Anhedral, skeletal dendrites; ilmenite oxidation lamellae are probably present and the titanomagnetite may be partially altered to maghemite; small size and skeletal form makes positive identification difficult | 2-4 | Largest opaque minerals are the Cr spinel inclusions in altered olivine phenocrysts; most Cr spinel inclusions have been replaced by titanomagnetite; olivine is replaced by Fe oxyhydroxide (iddingsite); no sulfide | 1206A-371, 1206A-372, 1206A-373 |
| 6 | 17R-2 (Piece 6, 74-76) | 100 |
Skeletal octahedra and dendrites; titanomagnetite is relatively unaltered with only modest development of ilmenite oxidation lamellae; maghemite is rarely developed along fractures | 8-10 | Cr spinel or chromite inclusions are present in altered olivines and are occasionally replaced by titanomagnetite; Fe oxyhydroxide is present in altered olivine phenocrysts; no sulfide | |
| 6 | 18R-1 (Piece 4, 49-51) | 50 |
Skeletal octahedra and dendrites; titanomagnetite is altered to maghemite along cleavage planes, fractures, and on crystal margins; ilmenite oxidation lamellae are present in unaltered titanomagnetite | 4-6 | Cr spinel is a discrete phenocryst phase (with thin overgrowths of titanomagnetite) and forms ~1% of the rock; it is also present as inclusions in olivine phenocrysts; no sulfide or Fe oxyhydroxide | 1206A-328, 1206A-331, 1206A-332, 1206A-333 |
| 6 | 18R-1 (Piece 4, 80-83) | 100 |
Skeletal octahedra and dendrites; development of ilmenite oxidation lamellae is extensive; maghemite is developed along fractures and cleavage planes, but some titanomagnetite crystals are maghemite free | 4-6 | Cr spinel is a discrete phenocryst phase (with thin overgrowths of titanomagnetite) and forms ~1% of the rock; it is also present as inclusions in olivine phenocrysts; olivine phenocrysts have a rim of Fe oxyhydroxide (iddingsite); no sulfide | 1206A-374, 1206A-375, 1206A-376, 1206A-377, 1206A-378, 1206A-379, 1206A-380 |
| 7 | 19R-3 (Piece 2, 46-48) | 10-150 | Skeletal octahedra and dendrites; mostly unaltered, but there is some development of ilmenite oxidation lamellae; maghemite is rarely present along fractures | 5-7 | A minor amount of secondary pyrite is present; no Fe oxyhydroxide | 1206A-334 |
| 8 | 21R-5 (Piece 9, 66-68) | — | Lobe margin; no titanomagnetite is present | — | Glass is now altered to a black-brown amorphous clay; no sulfide or Fe oxyhydroxide | |
| 10 | 24R-3 (Piece 2, 10-12) | 10-150 | Skeletal octahedra and dendrites; development of ilmenite oxidation lamellae is extensive; maghemite is developed along fractures and cleavage planes, but many titanomagnetite crystals are maghemite free | 4-6 | No sulfide or Fe oxyhydroxide | 1206A-335, 1206A-336 |
| 11 | 28R-1 (Piece 17C, 100-102) | — | Lobe margin; no titanomagnetite is present | — | Cr spinel inclusions are present in altered olivine phenocrysts; glass is now altered to a black-brown amorphous clay; no sulfide or Fe oxyhydroxide | 1206A-337 |
| 13 | 31R-1 (Piece 11, 60-63) | 20 |
Skeletal octahedra and dendrites; slight development of ilmenite oxidation lamellae; no maghemite | 4-6 | Cr spinel inclusions are present in altered olivine phenocrysts; olivine is replaced by Fe oxyhydroxide (iddingsite); no sulfide | 1206A-339 |
| 14 | 32R-2 (Piece 26, 136-137) | — | Lobe margin; no titanomagnetite is present | — | Glass is now altered to a black-brown amorphous clay; no sulfide or Fe oxyhydroxide | 1206A-367 |
| 17 | 38R-1 (Piece 2B, 55-58) | 50 |
Skeletal octahedra and dendrites plus anhedral masses; groundmass titanomagnetite is 50 µm; where it has replaced Cr spinel phenocrysts, it is between 150-250 µm; extensive development of ilmenite oxidation lamellae; no maghemite alteration |
8-10 | Cr spinel is present as inclusions in olivine phenocrysts and as discrete phenocrysts (now replaced by titanomagnetite); occasional Cr spinel relicts are present in the larger titanomagnetites; no sulfide or Fe oxyhydroxide | 1206A-349, 1206A-350, 1206A-360, 1206A-361, 1206A-362, 1206A-363, 1206A-364 |
| 18b | 41R-1 (Piece 5A, 22-24) | 150 |
Skeletal octahedra and dendrites; ilmenite oxidation lamellae are present; rare maghemite is developed along fractures | 7-9 | Cr spinel inclusions in altered olivine phenocrysts have mostly been replaced by titanomagnetite; no sulfide or Fe oxyhydroxide | 1206A-365, 1206A-366 |
| 21 | 42R-2 (Piece 3, 76-78) | 30 |
Subhedral octahedra; slight development of ilmenite oxidation lamellae; no maghemite | 9-11 | A minor amount of secondary pyrite is present; no Fe oxyhydroxide | 1206A-383 |