Klebelsbergite is a rare secondary antimony mineral that typically forms as delicate, acicular crystals or radiating sprays in the oxidation zones of antimony deposits. It is best identified by its adamantine luster and association with other secondary antimony minerals like valentinite. Due to its fragility and rarity, it is highly sought after by advanced systematic collectors.

Hardness

3.5-4

Mohs

Luster

Vitreous to silky

Streak

White to yellow

Transparency

Semitransparent

mineralrare

Klebelsbergite

Hardness: 3.5-4
Luster: Vitreous to silky
Streak: White to yellow
Transparency: Semitransparent

Is this klebelsbergite?

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 klebelsbergite with a known reference. Klebelsbergite sits at Mohs 3.5-4, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white to yellow.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous to silky.
4
Match the color range
Compare against the expected color range: colorless, yellow orange, white, light yellow, dark yellow.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: acicular crystals, radiating clusters, crusts.

Often confused with

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

mineral

Valentinite

Mohs 2.5-3

How to tell apart: Luster reads vitreous to silky on Klebelsbergite and adamantine, pearly on cleavages on Valentinite.

How to tell apart: Klebelsbergite is noticeably harder (Mohs 3.5-4 vs. 2-2.5); luster reads vitreous to silky on Klebelsbergite and resinous to subadamantine on Senarmontite.

How to tell apart: Stibiconite is the harder of the two (Mohs 5.5-7 vs. 3.5-4); streak differs, so Klebelsbergite leaves white to yellow, Stibiconite leaves light yellow; luster reads vitreous to silky on Klebelsbergite and pearly, opaline, glassy to earthy on Stibiconite.

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Often found alongside klebelsbergite

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

All properties

Chemical formula: Sb₄O₄(OH)₂SO₄
Mohs hardness: 3.5-4
Density: 4.62 g/cm³
Colors: Colorless Yellow orange White Light yellowDark yellow
Streak: White to yellow
Luster: Vitreous to silky
Transparency: Semitransparent
Crystal system: Orthorhombic
Crystal habit: Acicular crystals, radiating clusters, crusts
Cleavage: Perfect
Rarity: Rare
Uses: Collector
Host rock: An alteration product of stibnite in antimony deposits

Where rockhounds find klebelsbergite

Classic worldwide localities

Baia Sprie (Felsőbánya), Romania
Tuscany, at the Cetine mine, 20 km southwest of Siena, Italy
Pereta mine, Scansano, Italy
Micciano, near Larderello, Italy

Field-hunting tip

Where it forms: An alteration product of stibnite in antimony deposits. If you start seeing stibnite, valentinite, cervantite in float, you are in the right ground. Typical habit: acicular crystals, radiating clusters, crusts. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify klebelsbergite?+

Mohs hardness is 3.5-4. Luster: vitreous to silky. The streak is white to yellow. Common colors include colorless, yellow orange, white, light yellow.

Where is klebelsbergite found?+

Notable localities include Baia Sprie (Felsőbánya), Romania; Tuscany, at the Cetine mine, 20 km southwest of Siena, Italy; Pereta mine, Scansano, Italy; Micciano, near Larderello, Italy.

Is klebelsbergite safe to handle?+

Klebelsbergite contains antimony. Contains antimony which is toxic if ingested or inhaled as dust. Always wash hands after handling and avoid creating dust when cleaning specimens.

What rocks look like klebelsbergite?+

Klebelsbergite is most often confused with Valentinite, Senarmontite, Stibiconite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with klebelsbergite?+

Klebelsbergite commonly co-occurs with Stibnite, Valentinite, Cervantite, Kermesite, Stibiconite, Coquandite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does klebelsbergite form in?+

Where it forms: An alteration product of stibnite in antimony deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is klebelsbergite used for?+

Klebelsbergite is used in collector.

Find klebelsbergite on the map

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