How to identify Serpentinite with Magnetite Veins

To correctly identify Serpentinite with Magnetite Veins (Serpentinite (Mg,Fe)3Si2O5(OH)4 with Magnetite (Fe3O4)), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   Serpentinite matrix: typically shades of green (light to dark), greenish-black, yellowish-green, or mottled. Magnetite veins: dark gray to black.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Serpentinite matrix: greasy, waxy, silky (fibrous varieties), or dull. Magnetite veins: metallic.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Serpentinite matrix: often massive, fine-grained, sometimes fibrous (chrysotile), or platy (antigorite). Can feel smooth or slightly soapy. Magnetite veins: granular to massive, often sharp and distinct within the serpentinite.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Serpentine minerals are typically anhedral to subhedral, forming interlocking masses or fibrous aggregates. Magnetite forms euhedral to anhedral crystals, often granular within veins.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Serpentine minerals: variable, often poor or absent in massive varieties, good basal cleavage in antigorite, fibrous cleavage in chrysotile. Magnetite: no true cleavage, but exhibits octahedral parting.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Associated with ophiolite complexes, subduction zones, and suture zones where oceanic crust and upper mantle rocks have been obducted or tectonically emplaced. Also found in metamorphic terrains where ultramafic intrusions have undergone hydration.

Key Facts

Hardness

Serpentinite: 2.5-4 (Mohs). Magnetite: 5.5-6.5 (Mohs).

Specific Gravity

Serpentinite: 2.5-2.8 g/cm³. Magnetite: 5.17-5.18 g/cm³.

Crystal System

Serpentine minerals: Monoclinic (antigorite, lizardite) or Orthorhombic (chrysotile). Magnetite: Isometric.

Color

Serpentinite: Green, yellowish-green, blackish-green, mottled. Magnetite: Iron-black to dark gray.

Luster

Serpentinite: Greasy, waxy, silky, dull. Magnetite: Metallic to submetallic.

Transparency

Serpentinite: Translucent to opaque. Magnetite: Opaque.

Fracture

Serpentinite: Conchoidal to splintery. Magnetite: Uneven to subconchoidal.

Cleavage

Serpentine minerals: Variable, often poor or absent; fibrous in chrysotile. Magnetite: None, but octahedral parting is common.

Composition

Serpentinite: Hydrous magnesium iron silicate. Magnetite: Iron oxide.

Physical characteristics

• Crystal Habit: Serpentine: Massive, platy, fibrous, lamellar. Magnetite: Octahedral, granular, massive.
• Cleavage Type: Serpentine: Variable, often poor or absent; fibrous in chrysotile. Magnetite: None, but octahedral parting.
• Fracture Type: Serpentine: Conchoidal to splintery. Magnetite: Uneven to subconchoidal.
• Tenacity: Serpentine: Tough, sometimes brittle or flexible (chrysotile). Magnetite: Brittle.
• Luster Type: Serpentine: Greasy, waxy, silky, dull. Magnetite: Metallic to submetallic.

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