Andymcdonaldite is an extremely rare barium-potassium-iron silicate mineral found in the sanbornite deposits of California. It typically occurs as small, distinct prismatic crystals associated with other rare silicate phases in metamorphosed limestone environments.

Hardness

4-4.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrareEdingtonite Group family

Andymcdonaldite

Hardness: 4-4.5
Luster: Vitreous
Streak: White
Transparency: Transparent

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Is this andymcdonaldite?

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 andymcdonaldite with a known reference. Andymcdonaldite 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. Andymcdonaldite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Andymcdonaldite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: yellow, brown.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: prismatic crystals.

Often confused with

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

Often found alongside andymcdonaldite

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

All properties

Chemical formula: K₂Ca(Fe³⁺)₂(Si₆O₂₀)·8H₂O
Mohs hardness: 4-4.5
Density: 2.73 g/cm³
Colors: Yellow Brown
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Orthorhombic
Crystal habit: Prismatic Crystals
Cleavage: Good
Rarity: Rare
Uses: Collector
Host rock: Metamorphosed Limestone
Typical price: $50-300 per specimen

Where rockhounds find andymcdonaldite

Classic worldwide localities

Big Creek, Fresno County, California, USA

Field-hunting tip

Look in metamorphosed limestone country — that is the host setting where andymcdonaldite typically forms. If you start seeing sanbornite, walstromite, quartz in float, you are in the right ground. Field specimens usually show a prismatic crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify andymcdonaldite?+

Mohs hardness is 4-4.5. It typically shows a vitreous luster. The streak is white. Common colors include yellow, brown.

Where is andymcdonaldite found?+

Notable localities include Big Creek, Fresno County, California, USA.

How much is andymcdonaldite worth?+

Typical asking prices fall in the range of $50-300 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like andymcdonaldite?+

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

What minerals are found with andymcdonaldite?+

Andymcdonaldite commonly co-occurs with Sanbornite, Walstromite, Quartz, Fresnoite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does andymcdonaldite form in?+

Andymcdonaldite typically forms in metamorphosed limestone. Working float back to the host body is the standard way to chase a fresh occurrence.

What is andymcdonaldite used for?+

Andymcdonaldite is used in collector.

Find andymcdonaldite on the map

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