Crystal Magnesite

Chemical Formula

MgCO₃

Composition

Magnesium carbonate, commonly with some iron and calcium

Variable Formula

(Mg,Fe,Ca)CO₃

Color

Colorless, white, gray, yellow, brown, orange, light pink, light green

Streak

White

Hardness

3.5 - 4.5

Crystal System

Hexagonal

Crystal Forms 
and Aggregates

Magnesite is not common in well formed crystals. Crystals are rhombohedral, sometimes single but more commonly in groupings and as cleavage fragments. Crystals may also be groupings of thin hexagonal plates, or as prismatic crystals. The most common form of Magnesite is in massive, compact, porous masses that are dull in luster. Also occurs grainy, coxcomb, botryoidal, in groups of thin, prismatic needles, and as small rounded balls.

Transparency

Transparent to nearly opaque

Specific Gravity

3.0 - 3.3

Luster

Vitreous to dull

Cleavage

1,3 - rhombohedral

Fracture

Conchoidal to even

Tenacity

Brittle

Other ID Marks

1) Massive, porous specimens will stick to the tongue if licked.
2) Occasionally fluorescent blue or green.

Complex Tests

Effervesces in hot hydrochloric acid

In Group

Carbonates; Calcite Group

Environment

In metamorphic serpentine rock and hornfels, in hydrothermal deposits, and in sedimentary beds.
 

Rock Type

Sedimentary, Metamorphic

Popularity (1-4)

2

Prevalence (1-3)

2

Demand (1-3)

2