Buddingtonite is an ammonium-bearing feldspar typically found as a replacement product in hydrothermal environments. It usually occurs as massive, fine-grained aggregates and requires laboratory confirmation via X-ray diffraction or infrared spectroscopy for positive identification.
Is this buddingtonite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch buddingtonite with a known reference. Buddingtonite sits at Mohs 5.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light grey, yellow when impure.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: cryptocrystalline, pseudomorphous.
Often confused with
Buddingtonite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Buddingtonite leaves light grey, yellow when impure, Adularia leaves white.
How to tell apart: Streak differs, so Buddingtonite leaves light grey, yellow when impure, Albite leaves white.
How to tell apart: Streak differs, so Buddingtonite leaves light grey, yellow when impure, Sanidine leaves white.
Often found alongside buddingtonite
Minerals reported to co-occur with buddingtonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NH₄AlSi₃O₈
- Mohs hardness
- 5.5
- Density
- 2.32 g/cm³
- Streak
- Light grey, yellow when impure
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Cryptocrystalline, pseudomorphous
- Cleavage
- Good on {001}, distinct on {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A low-temperature hydrothermal replacement of plagioclase in andesite altered by ammonia-bearing hot springs (Sulfur Bank mine, California, USA); in metasomatized rhyolitic ash-flow tuffs (Cedar Mountains, Nevada, USA)
Where rockhounds find buddingtonite
Classic worldwide localities
- Sulfur Bank mercury mine, Lake Co., and on Sharon Heights, Menlo Park, Santa Clara Co., California, USA
- Cedar Mountains, 50 km northwest of Tonopah, Nye Co., Nevada, USA
- A number of exposures of the Meade Peak Member of the Phosphoria Formation in Idaho, Wyoming, Montana, USA
- Condor oilshale deposit, near Proserpine, Queensland, Australia
- Toshichi Spa, Iwate Prefecture, Japan
Field-hunting tip
Where it forms: A low-temperature hydrothermal replacement of plagioclase in andesite altered by ammonia-bearing hot springs (Sulfur Bank mine, California, USA); in metasomatized rhyolitic ash-flow tuffs (Cedar Mountains, Nevada, USA). If you start seeing plagioclase, sulfur, stibnite in float, you are in the right ground. Typical habit: cryptocrystalline, pseudomorphous. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify buddingtonite?+
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What rocks look like buddingtonite?+
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Find buddingtonite on the map
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