Locality Palette, 2026

A grayscale and colorized basaltic fragment sits above a Senegal map and mineral phase graph.

Locality Palette develops a provenance-anchored colorization method for nanoCT grayscale data. X-ray attenuation values record material density, not color. Grayscale volumes have no color ground truth. Neural colorization models trained on natural photographs assign color through texture similarity, mapping porous structures to whatever the training set associates with similar textures. Applied to scientific imaging, this is a category error: the output encodes learned associations, not specimen properties. The locality palette system instead derives color from the geological provenance of each scanned grain. Each collection site determines which minerals are present and at what density ranges they occur. Attenuation bands map to mineral phases characteristic of the provenance: basaltic glass and clinopyroxene for Stromboli tephra, quartz and iron oxides for Wilhelmshaven tidal sediment, feldspar and heavy minerals for Birimian coastal sand. The same attenuation value can represent different minerals at different sites: a quartz-dominated North Sea grain and a plagioclase-rich volcanic fragment occupy overlapping density ranges but carry different geological identities. Anchor colors for each locality reference published mineralogy and thin-section optical data. A lookup table interpolates between anchors to produce a continuous color mapping across the full attenuation range. False-color conventions in adjacent fields follow comparable logic: astronomical imaging maps wavelength bands to RGB channels through declared assignment, not observed color. The locality palette applies this principle to geological specimens, where every color traces to a stated mineral phase at a specific density range for a given provenance. The system does not resolve the fundamental problem of assigning color to data captured outside the visible spectrum. It makes the mapping assumptions explicit (which mineral, at which density, mapped to which color) rather than embedding them in learned weights. Localities span volcanic, metamorphic, carbonate, and siliciclastic provenances. The investigation remains ongoing.

A colorized nanoCT scan of specimen 24-PO-I displays an Fe-oxide matrix and Fe-stained silicate.
A colorized nanoCT scan of specimen 30 from Mallipo Beach displays a glauconite-bearing mineral grain.
A colorized nanoCT slice of sample 36-CB-II displays K-feldspar, quartz, and hornblende next to a Connecticut map.
A colorized nanoCT scan of a Miocene reef limestone sample from Mallorca sits next to a grayscale scan and a mineral phase chart.
A nanoCT scan shows a dark hornblende fragment with a mineral phase scale and a map of Rockaway Beach.
A nanoCT scan shows a curved limestone fragment and a map of Mallorca.
A colorized nanoCT scan shows a foraminifera test with calcite and iron-oxide staining in Nakdong delta sediment.
A colorized nanoCT scan of specimen 78 shows iron-stained quartz arenite with a goethite coating.
A colorized nanoCT scan of specimen 80 maps minerals like hematite and quartz using the Locality Palette.
A Locality Palette scan of Stromboli specimen 89 maps basaltic glass, plagioclase, and augite.

Photography: Phillip C. Reiner

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