RockHoundR

Indigo Gabbro is a coarse-grained igneous rock, often trade-named 'Mystic Merlinite', primarily sourced from Madagascar. It is characterized by its deep charcoal-to-indigo base color with swirling inclusions of grey and purple, which take a high polish in lapidary work.

Hardness
6-7
Mohs
Luster
Submetallic
Transparency
Opaque

Is this indigo gabbro?

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 indigo gabbro with a known reference. Indigo Gabbro sits at Mohs 6-7, softer than the next harder reference, harder than the previous one.
  • 2
    Read the texture
    Look at a fresh break with a hand lens. Texture: Phaneritic. Grain size: Coarse-grained.
  • 3
    Pick out the minerals
    Composition: Gabbro: mostly clinopyroxene and calcium-rich plagioclase. Identify the two or three most abundant grains.
  • 4
    Read the luster
    Hold the specimen under a strong light. Luster: submetallic.
  • 5
    Match the color range
    Compare against the expected color range: black, dark purple, gray.

Often confused with

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

Gabbro igneous
igneous
Gabbro
Mohs 6-7

How to tell apart: Luster reads submetallic on Indigo Gabbro and vitreous on Gabbro.

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Labradorite mineral
mineral
Labradorite
Mohs 6-6.5

How to tell apart: Luster reads submetallic on Indigo Gabbro and vitreous; pearly on cleavages on Labradorite.

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Often found alongside indigo gabbro

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

All properties

Mohs hardness
6-7
Density
2.8-3.1 g/cm³
Colors
BlackDark purpleGray
Luster
Submetallic
Transparency
Opaque
Rarity
Common
Uses
Lapidary, Collector, Decorative
Host rock
plutonic igneous rock
Texture
Phaneritic
Grain size
Coarse-grained
Composition
Gabbro: mostly clinopyroxene and calcium-rich plagioclase

Where rockhounds find indigo gabbro

Classic worldwide localities

  • Madagascar

Field-hunting tip

Where it forms: plutonic igneous rock. If you start seeing plagioclase, pyroxene, magnetite in float, you are in the right ground.

Common questions

How do you identify indigo gabbro?+
Mohs hardness is 6-7. Texture: Phaneritic. Composition: Gabbro: mostly clinopyroxene and calcium-rich plagioclase. Luster: submetallic. Common colors include black, dark purple, gray.
Where is indigo gabbro found?+
Notable localities include Madagascar.
What rocks look like indigo gabbro?+
Indigo Gabbro is most often confused with Gabbro, Labradorite. A quick hardness test and a streak check separate the look-alikes faster than color alone.
What minerals are found with indigo gabbro?+
Indigo Gabbro commonly co-occurs with Plagioclase, Pyroxene, Magnetite, Chlorite. Spotting any of these in float or country rock is a useful trip signal.
What kind of rock does indigo gabbro form in?+
Where it forms: plutonic igneous rock. Working float back to the host body is the standard way to chase a fresh occurrence.
What is indigo gabbro used for?+
Indigo Gabbro is used in lapidary, collector, decorative.

Find indigo gabbro on the map

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