Hydroxylgugiaite is an extremely rare beryllium-bearing silicate primarily found in the volcanic ejecta of the Eifel region in Germany. It typically occurs as small, transparent prismatic crystals within cavities of metamorphosed limestone xenoliths. Due to its scarcity and association with complex mineral assemblages, it is highly sought after by specialized systematic mineral collectors.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent to translucent

mineralrareMelilite Group family

Hydroxylgugiaite

Hardness: ~5
Luster: Vitreous
Streak: White
Transparency: Transparent to translucent

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Is this hydroxylgugiaite?

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 hydroxylgugiaite with a known reference. Hydroxylgugiaite sits at Mohs ~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: colorless, white, pale gray.
5
Look at form & habit
Crystal system: tetragonal. Typical habit: prismatic crystals.

Often confused with

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

Often found alongside hydroxylgugiaite

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

All properties

Chemical formula: Ca₂BeSi₂O₇(OH)₂
Mohs hardness: ~5
Density: 2.79 g/cm³
Colors: Colorless White Pale gray
Streak: White
Luster: Vitreous
Transparency: Transparent to translucent
Crystal system: Tetragonal
Crystal habit: Prismatic crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: A replacement of Be silicate minerals in hydrothermally-altered syenite pegmatite

Where rockhounds find hydroxylgugiaite

Classic worldwide localities

Larvik plutonic complex, at Blåfjell, Langangen and at the Saga I quarry, Mørje, Porsgrunn, Telemark, southern Norway, and on top of Mount Nakkaalaaq, Ilímaussaq alkaline complex, southern Greenland

Field-hunting tip

Where it forms: A replacement of Be silicate minerals in hydrothermally-altered syenite pegmatite. If you start seeing microcline, albite, biotite 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 hydroxylgugiaite?+

Mohs hardness is ~5. Luster: vitreous. The streak is white. Common colors include colorless, white, pale gray.

Where is hydroxylgugiaite found?+

Notable localities include Larvik plutonic complex, at Blåfjell, Langangen and at the Saga I quarry, Mørje, Porsgrunn, Telemark, southern Norway, and on top of Mount Nakkaalaaq, Ilímaussaq alkaline complex, southern Greenland.

Is hydroxylgugiaite safe to handle?+

Hydroxylgugiaite contains beryllium. Wash your hands afterwards, never grind or breathe the dust, and store it apart from specimens you handle often.

What rocks look like hydroxylgugiaite?+

Hydroxylgugiaite is most often confused with Gugiaite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with hydroxylgugiaite?+

Hydroxylgugiaite commonly co-occurs with Microcline, Albite, Biotite, Zircon, Pyrochlore, Fayalite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does hydroxylgugiaite form in?+

Where it forms: A replacement of Be silicate minerals in hydrothermally-altered syenite pegmatite. Working float back to the host body is the standard way to chase a fresh occurrence.

What is hydroxylgugiaite used for?+

Hydroxylgugiaite is used in collector.

Find hydroxylgugiaite on the map

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