Sewardite is a rare calcium-iron arsenate mineral primarily known from the legendary Tsumeb Mine in Namibia. It typically occurs as small, dark green platy crystals or crusts coating other minerals within the oxidation zone of arsenic-rich ore bodies.
Is this sewardite?
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 sewardite with a known reference. Sewardite sits at Mohs 3-4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Sewardite leaves a reddish brown streak.
- 3Read the lusterHold the specimen under a strong light. Sewardite typically shows a subadamantine luster.
- 4Match the color rangeCompare against the expected color range: dark green, yellow-green.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: platy crystals, crusts, radial aggregates.
Often confused with
Sewardite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Sewardite leaves reddish brown, Duftite leaves light green; luster reads subadamantine on Sewardite and vitreous on Duftite.
How to tell apart: Streak differs, so Sewardite leaves reddish brown, Conichalcite leaves light green; luster reads subadamantine on Sewardite and vitreous on Conichalcite.
How to tell apart: Streak differs, so Sewardite leaves reddish brown, Austinite leaves white; luster reads subadamantine on Sewardite and subadamantine to silky on Austinite.
Often found alongside sewardite
Minerals reported to co-occur with sewardite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaFe³⁺₂(AsO₄)₂(OH)₂
- Mohs hardness
- 3-4
- Density
- 4.16 g/cm³
- Colors
- Streak
- Reddish Brown
- Luster
- Subadamantine
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Platy Crystals, Crusts, Radial Aggregates
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Hydrothermal Lead-zinc-copper Deposits
Where rockhounds find sewardite
Classic worldwide localities
- Tsumeb Mine, Namibia
Field-hunting tip
Look in oxidized hydrothermal lead-zinc-copper deposits country, the host setting where sewardite typically forms. If you start seeing tsumcorite, arseniosiderite, goethite in float, you are in the right ground. Field specimens usually show a platy crystals, crusts, radial aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify sewardite?+
Where is sewardite found?+
Is sewardite safe to handle?+
What rocks look like sewardite?+
What minerals are found with sewardite?+
What kind of rock does sewardite form in?+
What is sewardite used for?+
Find sewardite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
