Merwinite is a rare nesosilicate mineral typically found in high-temperature contact metamorphic zones where limestones have been altered by igneous intrusions. It most commonly appears as colorless or pale green granular masses rather than well-defined crystals. It is a prized specimen for advanced collectors specializing in skarn mineralogy.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent to translucent

mineralrare

Merwinite

Hardness: 6
Luster: Vitreous
Streak: White
Transparency: Transparent to translucent

Is this merwinite?

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 merwinite with a known reference. Merwinite sits at Mohs 6, 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.
4
Match the color range
Compare against the expected color range: colorless, gray, pale green.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: granular.

Often confused with

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

Often found alongside merwinite

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

All properties

Chemical formula: Ca₃Mg(SiO₄)₂
Mohs hardness: 6
Density: 3.15-3.32 g/cm³
Colors: Colorless Gray Pale green
Streak: White
Luster: Vitreous
Transparency: Transparent to translucent
Crystal system: Monoclinic
Crystal habit: Granular
Cleavage: Perfect on {100}
Rarity: Rare
Uses: Collector
Host rock: In siliceous dolomitic limestone in contact metamorphic zones, formed at relatively elevated temperatures, locally in substantial quantities

Where rockhounds find merwinite

Classic worldwide localities

Crestmore, Riverside Co., California, USA
Neihart, Cascade Co., Montana, USA
Christmas Mountains, Brewster Co., Texas, USA
Velardeña, Durango, Mexico
Scawt Hill, near Larne, Co. Antrim, Ireland
Found near Anakit Creek, at the mouth of the Lower Tunguska River, central Siberia, and in the Ozerskii massif, Lake Baikal, Russia

Field-hunting tip

Where it forms: In siliceous dolomitic limestone in contact metamorphic zones, formed at relatively elevated temperatures, locally in substantial quantities. If you start seeing gehlenite, spurrite, monticellite in float, you are in the right ground. Typical habit: granular. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify merwinite?+

Mohs hardness is 6. Luster: vitreous. The streak is white. Common colors include colorless, gray, pale green.

Where is merwinite found?+

Notable localities include Crestmore, Riverside Co., California, USA; Neihart, Cascade Co., Montana, USA; Christmas Mountains, Brewster Co., Texas, USA; Velardeña, Durango, Mexico; Scawt Hill, near Larne, Co. Antrim, Ireland.

What rocks look like merwinite?+

Merwinite is most often confused with Monticellite, Larnite, Bredigite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with merwinite?+

Merwinite commonly co-occurs with Gehlenite, Spurrite, Monticellite, Vesuvianite, Spinel. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does merwinite form in?+

Where it forms: In siliceous dolomitic limestone in contact metamorphic zones, formed at relatively elevated temperatures, locally in substantial quantities. Working float back to the host body is the standard way to chase a fresh occurrence.

What is merwinite used for?+

Merwinite is used in collector.

Find merwinite on the map

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