Macdonaldite is a rare barium silicate mineral typically found in metamorphic environments associated with sanbornite. Collectors look for its characteristic bladed, white to colorless radial crystal sprays that exhibit a bright white fluorescence under short-wave ultraviolet light.
Is this macdonaldite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch macdonaldite with a known reference. Macdonaldite sits at Mohs 4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Macdonaldite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Macdonaldite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: bladed crystals, radial aggregates.
Often confused with
Macdonaldite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside macdonaldite
Minerals reported to co-occur with macdonaldite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- BaCa₄Si₁₆O₃₈(OH)₂·8H₂O
- Mohs hardness
- 4
- Density
- 2.28 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Bladed Crystals, Radial Aggregates
- Cleavage
- Perfect
- Fluorescence
- Bright White Under SW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metasomatized Sanbornite-bearing Rocks
- Typical price
- $20-150 thumbnail
Where rockhounds find macdonaldite
Classic worldwide localities
- Big Creek-Rush Creek area, Fresno County, California, USA
Field-hunting tip
Look in metasomatized sanbornite-bearing rocks country — that is the host setting where macdonaldite typically forms. If you start seeing sanbornite, walstromite, traskite in float, you are in the right ground. Field specimens usually show a bladed crystals, radial aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify macdonaldite?+
Where is macdonaldite found?+
How much is macdonaldite worth?+
What rocks look like macdonaldite?+
What minerals are found with macdonaldite?+
What kind of rock does macdonaldite form in?+
What is macdonaldite used for?+
Find macdonaldite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
