Aenigmatite is a complex sodium-iron-titanium silicate typically found in peralkaline igneous rocks. It is most easily identified by its dark, often black, prismatic crystals and high density compared to common amphiboles. Collectors usually hunt for it in syenite pegmatites or nepheline syenites where it occurs as a primary mineral.
Is this aenigmatite?
5-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 aenigmatite with a known reference. Aenigmatite sits at Mohs 5.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: reddish brown.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to greasy.
- 4Match the color rangeCompare against the expected color range: black, brown.
- 5Look at form & habitCrystal system: triclinic. Typical habit: lamellar.
Often confused with
Aenigmatite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Aenigmatite leaves reddish brown, Arfvedsonite leaves deep bluish gray, gray-green.
How to tell apart: Streak differs, so Aenigmatite leaves reddish brown, Hornblende leaves grayish-white.
How to tell apart: Streak differs, so Aenigmatite leaves reddish brown, Augite leaves gray-green.
Often found alongside aenigmatite
Minerals reported to co-occur with aenigmatite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₂Fe²⁺₅TiSi₆O₂₀
- Mohs hardness
- 5.5
- Density
- 3.81 g/cm³
- Streak
- Reddish brown
- Luster
- Vitreous to greasy
- Transparency
- Translucent to opaque
- Crystal system
- Triclinic
- Crystal habit
- Lamellar
- Cleavage
- Good on {010}, {100}
- Rarity
- Uncommon
- Uses
- Collector, Scientific research
- Host rock
- A primary constituent in sodium-rich alkalic volcanics, pegmatites, and other silica-poor igneous rocks
Where rockhounds find aenigmatite
Classic worldwide localities
- Granite Mountain, near Little Rock, Pulaski Co., Arkansas, and Santa Rosa, Sonoma Co., California, USA
- Khibiny and Lovozero massifs, Kola Peninsula, Russia
- Sandefjord, Norway
- Cuddua Mida, Sicily, Italy
- Warrumbungle volcano, Nandewar volcano, and the Mt. Warning complex, New South Wales, Australia
- Peak Range Province, Queensland, Australia
Field-hunting tip
Where it forms: A primary constituent in sodium-rich alkalic volcanics, pegmatites, and other silica-poor igneous rocks. If you start seeing aegirine, augite, riebeckite in float, you are in the right ground. Typical habit: lamellar. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify aenigmatite?+
Where is aenigmatite found?+
What rocks look like aenigmatite?+
What minerals are found with aenigmatite?+
What kind of rock does aenigmatite form in?+
What is aenigmatite used for?+
Find aenigmatite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
