Sekaninaite is the iron-dominant member of the cordierite group, typically occurring in granite pegmatites. It is often visually indistinguishable from cordierite without laboratory analysis, generally forming blue-violet prismatic crystals or granular aggregates within pegmatitic rocks.

Hardness

7-7.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent to translucent

mineralrareCordierite Group family

Sekaninaite

Hardness: 7-7.5
Luster: Vitreous
Streak: White
Transparency: Transparent to translucent

Is this sekaninaite?

5-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 sekaninaite with a known reference. Sekaninaite sits at Mohs 7-7.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: blue, blue violet, violet blue, gray blue.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: crystalline.

Often confused with

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

Often found alongside sekaninaite

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

All properties

Chemical formula: Fe₂Al₃(AlSi₅O₁₈)
Mohs hardness: 7-7.5
Density: 2.76-2.77 g/cm³
Colors: BlueBlue violetViolet blue Gray blue
Streak: White
Luster: Vitreous
Transparency: Transparent to translucent
Crystal system: Orthorhombic
Crystal habit: Crystalline
Cleavage: {100}, imperfect; parting on {001}
Rarity: Rare
Uses: Collector
Host rock: Pegmatitic rocks

Where rockhounds find sekaninaite

Classic worldwide localities

Brockley, Rathlin Island, Co. Antrim, Ireland
Gåsborn, Bergslagen, Sweden
Filone Rosina, Elba, Italy
Kitasugama, Fukushima Prefecture, Japan
Sasago and Doshi, Yamanashi Prefecture, Japan
Ide, Kyoto Prefecture, Japan

Field-hunting tip

Where it forms: Pegmatitic rocks. If you start seeing quartz, k-feldspar, biotite in float, you are in the right ground. Typical habit: crystalline. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify sekaninaite?+

Mohs hardness is 7-7.5. Luster: vitreous. The streak is white. Common colors include blue, blue violet, violet blue, gray blue.

Where is sekaninaite found?+

Notable localities include Brockley, Rathlin Island, Co. Antrim, Ireland; Gåsborn, Bergslagen, Sweden; Filone Rosina, Elba, Italy; Kitasugama, Fukushima Prefecture, Japan; Sasago and Doshi, Yamanashi Prefecture, Japan.

What rocks look like sekaninaite?+

Sekaninaite is most often confused with Cordierite, Indialite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with sekaninaite?+

Sekaninaite commonly co-occurs with Quartz, K-feldspar, Biotite, Garnet. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does sekaninaite form in?+

Where it forms: Pegmatitic rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is sekaninaite used for?+

Sekaninaite is used in collector.

Find sekaninaite on the map

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