Mascagnite is an ammonium sulfate mineral typically found as a sublimated crust around volcanic fumaroles or in areas of burning coal seams. It is highly water-soluble, meaning specimens must be kept in sealed containers in a dry, cool environment to prevent deliquescence or dissolution.

Hardness

2-2.5

Mohs

Luster

Vitreous to dull

Streak

White

Transparency

Transparent to translucent

mineraluncommon

Mascagnite

Hardness: 2-2.5
Luster: Vitreous to dull
Streak: White
Transparency: Transparent to translucent

Is this mascagnite?

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 mascagnite with a known reference. Mascagnite sits at Mohs 2-2.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous to dull.
4
Match the color range
Compare against the expected color range: white, colorless, gray, grayish yellow, yellow.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: stalactitic, water soluble.

Often confused with

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

Often found alongside mascagnite

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

All properties

Chemical formula: (NH₄)₂SO₄
Mohs hardness: 2-2.5
Density: 1.768 g/cm³
Colors: White Colorless Gray Grayish yellow Yellow
Streak: White
Luster: Vitreous to dull
Transparency: Transparent to translucent
Crystal system: Orthorhombic
Crystal habit: Stalactitic, water soluble
Cleavage: {100}, good
Rarity: Uncommon
Uses: Collector, Scientific
Host rock: A sublimation product in fumaroles and solfataras; formed by burning coal seams

Where rockhounds find mascagnite

Classic worldwide localities

Geysers, Sonoma Co., California, USA
Kehley’s Run mine, near Shenandoah, Schuylkill Co., and Glen Lyon, Luzerne Co., Pennsylvania, USA
Bitter Creek, near Wamsutter, Sweetwater Co., Wyoming, USA
Vesuvius, Campania, and Etna, Sicily, Italy
Volcanoes on the Kamchatka Peninsula, Russia
Clara mine, near Oberwolfach, Black Forest, and on the dump of the Paul-Berndt mine, Freital, Saxony, Germany

Field-hunting tip

Where it forms: A sublimation product in fumaroles and solfataras; formed by burning coal seams. If you start seeing sal ammoniac, tschermigite, sylvite in float, you are in the right ground. Typical habit: stalactitic, water soluble. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify mascagnite?+

Mohs hardness is 2-2.5. Luster: vitreous to dull. The streak is white. Common colors include white, colorless, gray, grayish yellow.

Where is mascagnite found?+

Notable localities include Geysers, Sonoma Co., California, USA; Kehley’s Run mine, near Shenandoah, Schuylkill Co., and Glen Lyon, Luzerne Co., Pennsylvania, USA; Bitter Creek, near Wamsutter, Sweetwater Co., Wyoming, USA; Vesuvius, Campania, and Etna, Sicily, Italy; Volcanoes on the Kamchatka Peninsula, Russia.

What rocks look like mascagnite?+

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

What minerals are found with mascagnite?+

Mascagnite commonly co-occurs with Sal ammoniac, Tschermigite, Sylvite, Halite, Sassolite, Boussingaultite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does mascagnite form in?+

Where it forms: A sublimation product in fumaroles and solfataras; formed by burning coal seams. Working float back to the host body is the standard way to chase a fresh occurrence.

What is mascagnite used for?+

Mascagnite is used in collector, scientific.

Find mascagnite on the map

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