Hennomartinite is a very rare manganese-strontium silicate that belongs to the pumpellyite group. It is primarily found in the metamorphosed manganese ore deposits of the Jacobsberg mine in Sweden, typically occurring as small granular masses.

Hardness

Mohs

Luster

Vitreous

Streak

Yellowish brown

Transparency

Translucent

mineralrarePumpellyite Group family

Hennomartinite

Hardness: ~4
Luster: Vitreous
Streak: Yellowish brown
Transparency: Translucent

Is this hennomartinite?

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 hennomartinite with a known reference. Hennomartinite sits at Mohs ~4, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: yellowish brown.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: brown, yellow brown.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: granular to massive.

Often found alongside hennomartinite

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

All properties

Chemical formula: SrMn₂Si₂O₇(OH)₂·H₂O
Mohs hardness: ~4
Density: 3.68 g/cm³
Colors: Brown Yellow brown
Streak: Yellowish brown
Luster: Vitreous
Transparency: Translucent
Crystal system: Orthorhombic
Crystal habit: Granular to massive
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: From a hand specimen, in veinlets of sérandite-pectolite cutting sugilite, probably of hydrothermal origin in a bedded manganese deposit

Where rockhounds find hennomartinite

Classic worldwide localities

Wessels mine, near Kuruman, Cape Province, South Africa

Field-hunting tip

Where it forms: From a hand specimen, in veinlets of sérandite-pectolite cutting sugilite, probably of hydrothermal origin in a bedded manganese deposit. If you start seeing sérandite-pectolite, sugilite, braunite in float, you are in the right ground. Typical habit: granular to massive. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify hennomartinite?+

Mohs hardness is ~4. Luster: vitreous. The streak is yellowish brown. Common colors include brown, yellow brown.

Where is hennomartinite found?+

Notable localities include Wessels mine, near Kuruman, Cape Province, South Africa.

What minerals are found with hennomartinite?+

Hennomartinite commonly co-occurs with Sérandite-pectolite, Sugilite, Braunite, Taikanite, Kornite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does hennomartinite form in?+

Where it forms: From a hand specimen, in veinlets of sérandite-pectolite cutting sugilite, probably of hydrothermal origin in a bedded manganese deposit. Working float back to the host body is the standard way to chase a fresh occurrence.

What is hennomartinite used for?+

Hennomartinite is used in collector.

Find hennomartinite on the map

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