Buddingtonite
Ammonium aluminosilicate (NH4AlSi3O8)
A rare ammonium feldspar formed by hydrothermal alteration, in which ammonium ions replace potassium, and a useful exploration indicator.
- Mohs hardness
- 5.5
- Color
- Colorless, white, or pale gray
- Type
- mineral
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Overview
Buddingtonite is a rare ammonium feldspar in which the ammonium ion (NH4+) takes the structural place normally occupied by potassium in feldspar, giving the composition NH4AlSi3O8 with some water. It is the only common natural feldspar built around ammonium.
It crystallizes in the monoclinic system and is typically colorless to white, occurring as fine-grained masses rather than large crystals. Named after the geologist Arthur F. Buddington, it forms in environments where ammonium-bearing fluids alter rocks.
Because ammonium in minerals usually comes from buried organic matter, buddingtonite is of interest both as a geochemical tracer of nitrogen and as a mineral that can be detected by remote infrared sensing.
Formation & geology
Buddingtonite forms by hydrothermal alteration of feldspar-bearing rocks by warm, ammonium-rich fluids, where the ammonium typically derives from the breakdown of organic matter in sediments. It is found around hot springs, in geothermal fields, and in altered volcanic and sedimentary rocks.
Classic occurrences include the Sulphur Bank mercury deposit in California (its type locality) and various epithermal gold systems, where ammonium released from carbonaceous host rocks reacts with feldspar. Its association with such systems makes it geologically significant out of proportion to its rarity.
How to identify it
Buddingtonite is colorless to white or pale gray, fine-grained, with hardness about 5.5, vitreous to dull luster, and white streak. It is essentially impossible to identify reliably by eye, as it resembles ordinary altered feldspar or clay.
It is diagnosed by its distinctive infrared absorption from the ammonium ion (N-H bonds), which allows detection by spectroscopy and even remote sensing, and confirmed by chemical or X-ray analysis. Its presence in hydrothermally altered, organic-rich settings is the main contextual clue.
Uses & significance
Buddingtonite has no industrial or gem use, but it is valuable as a mineral-exploration indicator. Its detection by infrared spectroscopy and remote sensing can help map hydrothermal alteration zones associated with epithermal gold deposits and geothermal systems.
Scientifically it is important to the geochemistry of nitrogen, recording the transfer of ammonium from buried organic matter into rock-forming minerals. It is collected by specialists but is not a display or lapidary material.
Frequently asked questions
What is buddingtonite?
It is a rare ammonium feldspar in which ammonium replaces potassium, formed by hydrothermal alteration with ammonium-rich fluids.
Why is buddingtonite useful in exploration?
It can be detected by infrared and remote sensing and marks hydrothermal alteration zones linked to epithermal gold deposits and geothermal systems.
Where does the ammonium in buddingtonite come from?
Usually from the breakdown of buried organic matter, whose nitrogen is converted to ammonium and incorporated into the feldspar structure.
Can you identify buddingtonite by sight?
Not reliably. It looks like ordinary white altered feldspar and requires infrared spectroscopy or chemical analysis for confirmation.
Buddingtonite guides
In-depth guides for identifying, valuing, and understanding Buddingtonite.
