Greenstone

Hardness: 3.5 to 5.0 (Mohs scale), Color: dull green to deep emerald green, Luster: waxy to dull, Structure: fine-grained and often massive or weakly foliated, Cleavage: poor.

Formed by low-grade regional metamorphism of mafic igneous rocks (like basalt or gabbro) under relatively low temperatures and pressures (Greenschist facies). Typical of Precambrian or Paleozoic eras.

Used as decorative stone, in construction as crushed stone, and historically for stone tools like celts or axes due to its toughness. Occasionally used in jewelry as 'greenstone' or 'New Zealand Jade' (though different from true Nephrite).

The green color comes from minerals like chlorite, epidote, or actinolite created during the metamorphism process. It is a major component of 'greenstone belts' which are prime targets for gold and silver mining.

Identify by its distinctive green hue (even when weathered), fine-grained texture, and lack of strong cleavage compared to slate. Common in ancient mountain-building sites or oceanic crust remnants.