Thénardite is a water-soluble sulfate mineral that typically forms as a dehydration product of mirabilite in arid climates. Collectors should note that it is highly sensitive to humidity and should be stored in a sealed container to prevent it from altering or crumbling.
Is this thénardite?
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 thénardite with a known reference. Thénardite sits at Mohs 2.5-3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to resinous.
- 4Match the color rangeCompare against the expected color range: white, grayish white, yellowish white, reddish white, brownish white.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: encrustations, prismatic, tabular.
Often confused with
Thénardite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside thénardite
Minerals reported to co-occur with thénardite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₂SO₄
- Mohs hardness
- 2.5-3
- Density
- 2.664 g/cm³
- Streak
- White
- Luster
- Vitreous to resinous
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Encrustations, prismatic, tabular
- Cleavage
- On {010}, perfect; on {101}, fair; on {100}, interrupted
- Fluorescence
- Bright white under SW and LW UV
- Rarity
- Common
- Uses
- Collector
- Host rock
- Typically in lacustrine (salt and soda lake) evaporite deposits in arid regions, also as crusts and efflorescences, which may be ephemeral, in a wide range of geologic environments; as precipitates around fumaroles
Where rockhounds find thénardite
5 mapped spotsClassic worldwide localities
- Searles Lake, San Bernardino Co., at Soda Lake, Carrizo Plain, San Luis Obispo Co., and from Bertram Siding, near the Salton Sea, Imperial Co., California, USA
- Camp Verde, Yavapai Co., Arizona, USA
- Kilauea Crater, Mauna Loa volcano, Hawaii, USA
- Espartinas salt lake, near Aranjuez, Madrid Province, Spain
- Vesuvius, Campania, and Etna, Sicily, Italy
- Natron Lakes, northwest of Cairo, Egypt
Field-hunting tip
Where it forms: Typically in lacustrine (salt and soda lake) evaporite deposits in arid regions, also as crusts and efflorescences, which may be ephemeral, in a wide range of geologic environments; as precipitates around fumaroles. If you start seeing mirabilite, blödite, glauberite in float, you are in the right ground. Typical habit: encrustations, prismatic, tabular. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Utah, North Dakota. Start trip planning there.
Common questions
How do you identify thénardite?+
Where is thénardite found?+
Can I find thénardite in the United States?+
What rocks look like thénardite?+
What minerals are found with thénardite?+
What kind of rock does thénardite form in?+
What is thénardite used for?+
Find thénardite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
