Afwillite is a rare calcium silicate hydrate often found as colorless to white prismatic crystals or radial clusters. It is primarily known to collectors from its classic occurrences in the Dutoitspan diamond mine and high-temperature metamorphic skarns. Its specific cleavage and unique mineral associations are key for identifying this relatively obscure species.
Is this afwillite?
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 afwillite with a known reference. Afwillite sits at Mohs 3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Afwillite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Afwillite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic crystals, radial aggregates, massive.
Often confused with
Afwillite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Afwillite is noticeably harder (Mohs 3 vs. 2).
How to tell apart: Okenite is the harder of the two (Mohs 4.5-5 vs. 3); luster reads vitreous on Afwillite and pearly on Okenite.
How to tell apart: Prehnite is the harder of the two (Mohs 6-6.5 vs. 3).
Often found alongside afwillite
Minerals reported to co-occur with afwillite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₃Si₂O₄(OH)₆
- Mohs hardness
- 3
- Density
- 2.63 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic Crystals, Radial Aggregates, Massive
- Cleavage
- Perfect On {100}, Good On {001}
- Rarity
- Rare
- Uses
- Collector, Research
- Host rock
- Hydrothermal Contact Metamorphic Zones and High-temperature Altered Rocks
- Typical price
- $20-150 for thumbnail specimens
Where rockhounds find afwillite
Classic worldwide localities
- Dutoitspan Mine, South Africa
- Scawt Hill, Northern Ireland
- Negev Desert, Israel
- Flekkefjord, Norway
Field-hunting tip
Look in hydrothermal contact metamorphic zones and high-temperature altered rocks country — that is the host setting where afwillite typically forms. If you start seeing calcite, ettringite, portlandite in float, you are in the right ground. Field specimens usually show a prismatic crystals, radial aggregates, massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find afwillite on the map
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