The Ferrous Minerals Ratio: Tracing Iron in the Rocks
Iron-bearing minerals leave a fingerprint in how they absorb near-infrared relative to shortwave-infrared, and the ferrous ratio reads that fingerprint to highlight iron-rich lithologies and alteration.
What it actually measures
The ratio increases where ferrous-iron absorption depresses NIR relative to SWIR. It complements the iron-oxide ratio, which targets ferric (oxidised) iron — together they bracket the iron mineralogy of a scene.
How it is calculated
where SWIR1 is shortwave-infrared 1 reflectance (~1.6 µm), NIR is near-infrared reflectance.
What the numbers mean
High values indicate ferrous (Fe²⁺-bearing) minerals through their SWIR absorption relative to NIR.
Band configuration
| Sentinel-2 | SWIR1 B11 · NIR B8 |
| Landsat 8/9 | SWIR1 B6 · NIR B5 |
Where it is used
Exploration geologists use it alongside the clay and iron-oxide ratios in band-ratio composites to map alteration and prospective lithologies.
Limitations to know
Like all band ratios it is broad and non-specific, easily muted by vegetation and sensitive to illumination and atmosphere — best used in arid, well-exposed terrain and always cross-checked with the other mineral ratios.
Compute Ferrous Minerals on your own study area
Skip the code. Draw or upload a boundary and Spatial Research Suite runs Ferrous Minerals on live Sentinel-2 or Landsat imagery — with cloud masking, exports and citations built in.
Run this analysis in GISforus →Frequently asked
What is the difference between ferrous and iron-oxide ratios?
The ferrous ratio targets reduced (Fe²⁺) iron via SWIR/NIR behaviour; the iron-oxide ratio targets oxidised (ferric) iron via red/blue. They are complementary.
Why combine mineral ratios?
Each is broad and non-specific, so geologists stack clay, ferrous and iron-oxide ratios to build a more confident alteration map.