Columbite-(Mg) is a rare member of the columbite group, specifically distinguished by its magnesium dominance in the site. Collectors usually look for its characteristic dark, tabular, or prismatic crystals embedded within coarse-grained granite pegmatites.
Is this columbite-(mg)?
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 columbite-(mg) with a known reference. Columbite-(Mg) sits at Mohs 6.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: dark brown.
- 3Read the lusterHold the specimen under a strong light. Luster: submetallic.
- 4Match the color rangeCompare against the expected color range: black, brownish black.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular, tabular.
Often confused with
Columbite-(Mg) vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Columbite-(Mg) leaves dark brown, Columbite-(Fe) leaves blackish brown.
How to tell apart: Streak differs, so Columbite-(Mg) leaves dark brown, Columbite-(Mn) leaves reddish black.
How to tell apart: Streak differs, so Columbite-(Mg) leaves dark brown, Tantalite leaves black to reddish-brown.
Often found alongside columbite-(mg)
Minerals reported to co-occur with columbite-(mg). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- MgNb₂O₆
- Mohs hardness
- 6.5
- Density
- 5.04 g/cm³
- Colors
- Streak
- Dark brown
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular, tabular
- Cleavage
- Indistinct on {010}; indistinct on {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In a pegmatite in partially assimilated dolomitic marbles
Where rockhounds find columbite-(mg)
Classic worldwide localities
- Kukhi-Lal deposit, southwestern Pamir Mountains, Tadzhikistan (type locality)
Field-hunting tip
Where it forms: In a pegmatite in partially assimilated dolomitic marbles. If you start seeing microcline, albite, beryl in float, you are in the right ground. Typical habit: acicular, tabular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify columbite-(mg)?+
Where is columbite-(mg) found?+
Is columbite-(mg) safe to handle?+
What rocks look like columbite-(mg)?+
What minerals are found with columbite-(mg)?+
What kind of rock does columbite-(mg) form in?+
What is columbite-(mg) used for?+
Find columbite-(mg) on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
