Grandite is a solid-solution series between the garnet species grossular and andradite. It typically occurs as brown to reddish-brown dodecahedral crystals in contact metamorphic zones known as skarns.

Hardness

6.5-7.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Translucent

mineralrareGarnet Group family

Grandaite

Hardness: 6.5-7.5
Luster: Vitreous
Streak: White
Transparency: Translucent

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Is this grandaite?

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 grandaite with a known reference. Grandaite sits at Mohs 6.5-7.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Grandaite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Grandaite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: brown, reddish-brown.
5
Look at form & habit
Crystal system: cubic. Typical habit: dodecahedral crystals, massive.

Often confused with

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

Often found alongside grandaite

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

All properties

Chemical formula: Ca₃Al₂Si₃O₁₂
Mohs hardness: 6.5-7.5
Density: 3.8-3.9 g/cm³
Colors: Brown Reddish-brown
Streak: White
Luster: Vitreous
Transparency: Translucent
Crystal system: Cubic
Crystal habit: Dodecahedral Crystals, Massive
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Skarn
Typical price: $20-150 for small specimens

Where rockhounds find grandaite

Classic worldwide localities

Mexico
United States

Field-hunting tip

Look in skarn country, the host setting where grandaite typically forms. If you start seeing calcite, diopside, vesuvianite in float, you are in the right ground. Field specimens usually show a dodecahedral crystals, massive habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify grandaite?+

Mohs hardness is 6.5-7.5. It typically shows a vitreous luster. The streak is white. Common colors include brown, reddish-brown.

Where is grandaite found?+

Notable localities include Mexico; United States.

How much is grandaite worth?+

Typical asking prices fall in the range of $20-150 for small specimens. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like grandaite?+

Grandaite is most often confused with Grossularite Garnet, Andradite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with grandaite?+

Grandaite commonly co-occurs with Calcite, Diopside, Vesuvianite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does grandaite form in?+

Grandaite typically forms in skarn. Working float back to the host body is the standard way to chase a fresh occurrence.

What is grandaite used for?+

Grandaite is used in collector.

Find grandaite on the map

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