Mccrillisite is an extremely rare phosphate mineral known primarily from the Mount Mica pegmatite in Maine. It typically forms as small, tabular crystals associated with other phosphate minerals in complex pegmatitic environments.

Hardness

4-4.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Translucent to transparent

mineralrare

Mccrillisite

Hardness: 4-4.5
Luster: Vitreous
Streak: White
Transparency: Translucent to transparent

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Is this mccrillisite?

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 mccrillisite with a known reference. Mccrillisite sits at Mohs 4-4.5, 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.
5
Look at form & habit
Crystal system: tetragonal. Typical habit: crystalline.

Often confused with

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

mineral

Beryllonite

Mohs 5.5-6

How to tell apart: Beryllonite is the harder of the two (Mohs 5.5-6 vs. 4-4.5).

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Often found alongside mccrillisite

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

All properties

Chemical formula: NaCsBeZr₂(PO₄)₄·1-2H₂O
Mohs hardness: 4-4.5
Density: 3.125 g/cm³
Colors: Colorless White
Streak: White
Luster: Vitreous
Transparency: Translucent to transparent
Crystal system: Tetragonal
Crystal habit: Crystalline
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: A rare product of late-stage hydrothermal alteration of primary zirconium-bearing minerals, in a complex granite pegmatite

Where rockhounds find mccrillisite

Classic worldwide localities

Mt. Mica, near Paris, Oxford Co., Maine, USA

Field-hunting tip

Where it forms: A rare product of late-stage hydrothermal alteration of primary zirconium-bearing minerals, in a complex granite pegmatite. If you start seeing zircon, kosnarite, roscherite 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 mccrillisite?+

Mohs hardness is 4-4.5. Luster: vitreous. The streak is white. Common colors include colorless, white.

Where is mccrillisite found?+

Notable localities include Mt. Mica, near Paris, Oxford Co., Maine, USA.

Is mccrillisite safe to handle?+

Mccrillisite 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 mccrillisite?+

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

What minerals are found with mccrillisite?+

Mccrillisite commonly co-occurs with Zircon, Kosnarite, Roscherite, Moraesite, Eosphorite, Löllingite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does mccrillisite form in?+

Where it forms: A rare product of late-stage hydrothermal alteration of primary zirconium-bearing minerals, in a complex granite pegmatite. Working float back to the host body is the standard way to chase a fresh occurrence.

What is mccrillisite used for?+

Mccrillisite is used in collector.

Find mccrillisite on the map

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