Magnesio-foitite is a rare member of the tourmaline group defined by a vacancy in the X-site of its crystal structure. Collectors typically find it as small, pale bluish gray or violet prismatic crystals embedded in pegmatite matrices. It is physically similar to other tourmalines and often requires chemical analysis for definitive identification.

Hardness

Mohs

Transparency

Transparent to translucent

mineralrareTourmaline Group family

Magnesio-foitite

Hardness: ~7
Transparency: Transparent to translucent

Is this magnesio-foitite?

3-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch magnesio-foitite with a known reference. Magnesio-foitite sits at Mohs ~7, softer than the next harder reference, harder than the previous one.
2
Match the color range
Compare against the expected color range: pale bluish gray.
3
Look at form & habit
Crystal system: trigonal. Typical habit: prismatic crystals.

Often confused with

Magnesio-foitite vs. its common look-alikes, and how to tell them apart in the field.

Often found alongside magnesio-foitite

Minerals reported to co-occur with magnesio-foitite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: ☐(Mg₂Al)Al₆Si₆O₁₈(BO₃)₃(OH)₄
Mohs hardness: ~7
Density: 2.995 g/cm³
Colors: Pale bluish gray
Transparency: Transparent to translucent
Crystal system: Trigonal
Crystal habit: Prismatic crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: From an alteration zone in a silicified porphyry developed in completely altered andesitic to dacitic volcanic rocks (Japan); in unconformity-type uranium deposits (Canada)

Where rockhounds find magnesio-foitite

Classic worldwide localities

Kyonosawa, Mitomi-mura, Higashi-Yamanashi-gun, Yamanashi-ken Prefecture, Honshu, ~100 km west of Tokyo, Japan
Rabbit Lake and Second Link Lake, eastern edge of the Athabasca Basin, Saskatchewan, Canada

Field-hunting tip

Where it forms: From an alteration zone in a silicified porphyry developed in completely altered andesitic to dacitic volcanic rocks (Japan); in unconformity-type uranium deposits (Canada). If you start seeing hematite, pyrite, rutile in float, you are in the right ground. Typical habit: prismatic crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify magnesio-foitite?+

Mohs hardness is ~7. Common colors include pale bluish gray.

Where is magnesio-foitite found?+

Notable localities include Kyonosawa, Mitomi-mura, Higashi-Yamanashi-gun, Yamanashi-ken Prefecture, Honshu, ~100 km west of Tokyo, Japan; Rabbit Lake and Second Link Lake, eastern edge of the Athabasca Basin, Saskatchewan, Canada.

What rocks look like magnesio-foitite?+

Magnesio-foitite is most often confused with Dravite, Schorl, Foitite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with magnesio-foitite?+

Magnesio-foitite commonly co-occurs with Hematite, Pyrite, Rutile, Quartz, Epidote, Dravitic tourmaline. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does magnesio-foitite form in?+

Where it forms: From an alteration zone in a silicified porphyry developed in completely altered andesitic to dacitic volcanic rocks (Japan); in unconformity-type uranium deposits (Canada). Working float back to the host body is the standard way to chase a fresh occurrence.

What is magnesio-foitite used for?+

Magnesio-foitite is used in collector.

Find magnesio-foitite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.