Importance. The primary economic value of tuff is as a building material. In the ancient world, tuff’s relative softness meant that it was commonly used for construction where it was available. Tuff is common in Italy, and the Romans used it for many buildings and bridges.

Tuff, a relatively soft, porous rock that is usually formed by the compaction and cementation of volcanic ash or dust. (The Italian term tufa is sometimes restricted to the soft, porous, sedimentary rock formed by the chemical deposition of calcite, or calcium carbonate, or silica from water as sinter.)

Volcanic tuff is a type of igneous rock, formed from material ejected during an explosive volcanic eruption.

Tuff cones are sometimes called ash cones. When heated rapidly by lava, water flashes to steam and expands violently, fragmenting huge amounts of lava into plumes of very fine grains of ash. This ash falls around the volcanic vent, creating an ash cone. Over time, the ash weathers into a rock known as tuff.

Tuff is an igneous rock with pyroclastic texture. Tuffs consist of fine-grained fragments created during volcanic eruptions. Some larger fragments are visible in this specimen.

The green color is due to the large development of chlorite. Among the crystalline schists of many regions, green beds or green schists occur, which consist of quartz, hornblende, chlorite or biotite, iron oxides, feldspar, etc., and are probably recrystallized or metamorphosed tuffs.

Obsidian is quite unique due to its smooth, uniform volcanic glass texture. Obsidian is usually considered an extrusive rock, because it usually solidifies above Earth’s surface where the edges of a lava flow come into contact with cool air or water. One of the most unique features of obsidian is how it breaks.

A strongly protective stone, Obsidian forms a shield against negativity, providing a grounding cord from the base chakra to the center of the earth. It absorbs negative energy from the environments and blocks psychic attack and negative spiritual influences. Obsidian brings clarity to the mind and clears confusion.

Scientists have known for more than 20 years that burning has an effect on obsidian – the dark, glossy volcanic glass that Native Americans often used to make knives, arrow points, and other flaked stone tools. Moist soils and temperatures below 100 degrees Celcius seemed to have little effect on obsidian hydration.