Magnesio-hornblende is a common member of the amphibole group, typically occurring as dark, elongated prismatic crystals in igneous and metamorphic rocks. It is most easily identified in the field by its distinct cleavage angles and vitreous luster. It is a major constituent of many common rock types but is usually valued by collectors for its well-formed, terminated crystals.
Is this magnesio-hornblende?
4-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 magnesio-hornblende with a known reference. Magnesio-hornblende sits at Mohs 5-6, softer than the next harder reference, harder than the previous one.
- 2Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 3Match the color rangeCompare against the expected color range: dark green, green.
- 4Look at form & habitCrystal system: monoclinic. Typical habit: prismatic crystals, elongated, bladed, massive.
Often confused with
Magnesio-hornblende vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside magnesio-hornblende
Minerals reported to co-occur with magnesio-hornblende. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂(Mg₄Al)(Si₇Al)O₂₂(OH)₂
- Mohs hardness
- 5-6
- Density
- 3.137 g/cm³
- Colors
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic crystals, elongated, bladed, massive
- Cleavage
- Good on {110}, with intersections at ~56° and ~124°
- Rarity
- Common
- Uses
- Collector, Petrology study
- Host rock
- A rock-forming mineral
Where rockhounds find magnesio-hornblende
Classic worldwide localities
- Sand dunes of Lüderitz, Karas Region, Namibia
Field-hunting tip
Where it forms: A rock-forming mineral. If you start seeing quartz, plagioclase, biotite in float, you are in the right ground. Typical habit: prismatic crystals, elongated, bladed, massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify magnesio-hornblende?+
Where is magnesio-hornblende found?+
What rocks look like magnesio-hornblende?+
What minerals are found with magnesio-hornblende?+
What kind of rock does magnesio-hornblende form in?+
What is magnesio-hornblende used for?+
Find magnesio-hornblende on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
