Oxyphlogopite is a rare member of the mica group characterized by the substitution of hydroxyl ions by oxygen, typically resulting from oxidation in high-temperature volcanic environments. It is physically similar to common phlogopite but can often be distinguished by its deeper reddish-brown hues and specific geological occurrence within volcanic ejecta.
Is this oxyphlogopite?
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 oxyphlogopite with a known reference. Oxyphlogopite sits at Mohs 3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: brown.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: dark brown, black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, scaly aggregates, disseminated flakes.
Often confused with
Oxyphlogopite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Oxyphlogopite leaves brown, Phlogopite leaves white; luster reads vitreous on Oxyphlogopite and pearly to submetallic on cleavage on Phlogopite.
How to tell apart: Streak differs, so Oxyphlogopite leaves brown, Biotite leaves white; luster reads vitreous on Oxyphlogopite and splendent to submetallic, vitreous, pearly on cleavage on Biotite.
How to tell apart: Streak differs, so Oxyphlogopite leaves brown, Annite leaves brownish white.
Often found alongside oxyphlogopite
Minerals reported to co-occur with oxyphlogopite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K(Mg,Ti,Fe,Fe)₃[(Si,Al)₄O₁₀](O,F)₂
- Mohs hardness
- 3
- Density
- 3.06 g/cm³
- Colors
- Streak
- Brown
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular crystals, scaly aggregates, disseminated flakes
- Cleavage
- Perfect on {001}
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- Pneumatolytic crystals coat vugs in alkaline basalt
Where rockhounds find oxyphlogopite
Classic worldwide localities
- Bartoy volcanic field, Transbaikalia, Russia (3T)
Field-hunting tip
Where it forms: Pneumatolytic crystals coat vugs in alkaline basalt. If you start seeing nepheline, plagioclase, sanidine in float, you are in the right ground. Typical habit: tabular crystals, scaly aggregates, disseminated flakes. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify oxyphlogopite?+
Where is oxyphlogopite found?+
What rocks look like oxyphlogopite?+
What minerals are found with oxyphlogopite?+
What kind of rock does oxyphlogopite form in?+
What is oxyphlogopite used for?+
Find oxyphlogopite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
