Physical Characteristics of Marcasite
chemical formula: FeS2
Hardness 6-6.5
Uneven fracture
Luster: Metallic
Color: pale bronze-yellow to almost white darkening on exposure
Streak: grayish black

Different structure “petals” usually called cockscomb
Generally it stays close to the ideal formula but can have minor Copper substitutions for iron and As for Sulfur

Resembles pyrite but has different crystal habit and is someone paler colored if fresh

Marcasite is common in hydrothermal sulfide deposits at low temperatures and is usually associated with galena and sphalerite. Concretionary masses in shale limestone and coal are also common.

It can replace the material in fossils which can make for beautiful samples

Not normally of economic value. (but can be used as a source of sulfur and iron)

Metaphysical properties:

The non-crystalline form posses the same properties as pyrite…

It provides you with a view of yourself from an outside perspective and can produce insight with respect to the methods available for correcting the qualities which are unwanted. Marcasite shows you if you appear dull to others and encourages you to shine.

It also illuminates the senses and the intellect softening expressiveness and dispelling both the use of rash words and the actions of impatience. It represents spiritual development, providing for prosperity of eliminating starvation of the spirit.

(1) Introduction to Mineralogy, by William D. Nesse
(2) Love is in the earth, a kaleidoscope of crystals, by Melody