trigonal Oxides
Hematite (Specularite)
Formula Fe2O3
Crystal Structure
#! Species: Hematite (Fe2O3)
#! System: Trigonal (-3m)
#! Habit: Tabular to platy crystals; massive specularite
trigonal[-3m]:{0001}@1.0 + {10-10}@0.5
trigonal
-3m
{0001} {10-10}
Quick Facts
Hardness
5.5
Specific Gravity
5.0
Optical Character
Opaque (metallic)
Physical Properties
- Crystal System
- trigonal
- Hardness (Mohs)
- 5.5
- Specific Gravity
- 5.0
- Cleavage
- None (parting in some directions)
- Fracture
- Conchoidal to uneven
- Lustre
- Metallic (specularite); sub-metallic to dull (earthy)
Optical Properties
- Optical Character
- Opaque (metallic)
- Pleochroism
- None (opaque)
Characteristics
Colours
Steel-grey to black (specularite/gem-quality)Red to red-brown (earthy/powdered form always red)
Localities
Brazil (Minas Gerais; iron quadrangle; major specularite source)Cumberland, England (Cleator Moor; historically significant)Elba, Italy (historical source; type locality for fine crystals)Lake Superior (USA/Canada; iron ore deposits)Namibia, Morocco (commercial)
Common Inclusions
Lamellar ilmenite intergrowthsConcentric internal growth banding (botryoidal kidney ore)
Known Treatments
Hematine (pressed simulant, strongly magnetic — not a treatment of hematite itself but a common trade confusion)
Crystal Forms
tabularmassivebotryoidal
Diagnostic Features
Red streak on unglazed porcelain tile (primary diagnostic despite metallic grey appearance); high SG 5.0-5.3; non-magnetic (contrast with hematine which IS magnetic); metallic mirror lustre; isostructural with corundum
Notes
Fe2O3; trigonal -3m; isostructural with corundum (Al2O3). Red streak is diagnostic despite metallic grey appearance. RI not measurable on refractometer (opaque). Non-magnetic — contrast with hematine (pressed iron powder simulant, strongly attracted to neodymium magnet). Castroviejo (2023) mineralogical reference (DOI 10.1007/978-3-031-12654-3_60) [VERIFIED] confirms crystal system, chemistry, and oxide group classification. SG and hardness from Read 7th ed. (DOI 10.4324/9780080507224) [PARTIALLY_SUPPORTED]. Gem material is the specular silvery variety (specularite); kidney ore is botryoidal. Hematine (synthetic/pressed) is the common simulant — detected by strong magnetism.
Related Minerals
Other minerals in the trigonal system
