What is pitchstone?

pitchstone obsidian arran
What is pitchstone?

How is pitchstone formed?

Is pitchstone just a special variation of volcanic glass? A form of obsidian rock created in high water conditions such as underwater in the sea?

Is pitchstone from the same source as lava rock around it but it has been transformed or transmuted by another process leaving or adding the high water content found in its chemical composition? Such as on the Isle of Arran, Isle of Skye, Scotland or Specimen Mountain, Colorado?

What is pitchstone, is it obsidian glass?

pitchstone Specimen Mountain Isle of Arran Scotland
Pitchstone found on Specimen Mountain, Colorado, USA

Pitchstone is a dull black glassy volcanic rock formed when a felsic, viscous lava or magma cools quickly. It is similar to obsidian but is defined by the International Union of Geological Sciences as having a higher water content. It is a volcanic glass, however, unlike a glass pitchstone has an irregular, hackly fracture not a conchoidal fracture, this is due to its coarser (than obsidian) crystal structure. pitchstone has a resinous lustre, or silky in some cases, and a variable composition. Its colour may be mottled, streaked, or uniform brown, red, green, gray, or black. It is an extrusive rock that is very resistant to erosion.
Pitchstone | wikipedia

Pitchstone formed in geology dikes and water or sea water?

pitchstone 7 specimen mountain never summer range volcanic glass
Pitchstone found on Specimen Mountain, Colorado, USA

Pitchstone is a glassy, acidic igneous rock, rather like obsidian but with a rather more waxy or resinous lustre owing to the absorption of water. The rock is glassy due to rapid quenching of the initial intrusion/extrusion.

When cooled very quickly, the magma has little or no time for crystals to grow and what results is largely a volcanic glass. Pitchstone often also exhibits flow-banding, well developed columnar jointing and the effects of devitrification.
Igneous Rocks - Pitchstone | University of Glasgow

It differs from obsidian principally in its rather dull lustre, for obsidian is bright and vitreous in appearance; all pitchstones also contain a considerable quantity of water in combination amounting to from 5 to 10% of their weight or 10% to 20% of their volume. The majority of the rocks of this class occur as intrusive dikes or veins; they are glassy forms of quartz porphyry and other dike rocks. Their dull lustre may be connected with the great abundance of minute crystallites and microlites they nearly always contain.
Pitchstone | Encyclopedia Britannica (1911)

pitchstone Specimen Mountain Isle of Arran Scotland

Most pitchstone occurs as dikes or marginal phases of dikes and therefore may grade into porphyry. Pitchstone porphyry (vitrophyre) consists of a glassy base (groundmass) enclosing abundant large crystals (phenocrysts) of such minerals as quartz, alkali feldspar, and plagioclase, as well as fewer crystals of pyroxene or hornblende. Pitchstone may reveal evidence of fluid flow by the presence of wavy streaks and trains of crystals; in pitchstone dikes, the lines and layers of flowage are oriented parallel to the dike walls.
Pitchstone - Natural glass | Britannica

pitchstone
Great Pitchstone Sill found on the Isle of Arran, Scotland

Pitchstone is richer in water than are obsidian and most other glassy rocks, generally containing 4 to 10 percent by weight; most of this water may have been absorbed from the sea or wet sediments into which the pitchstone was intruded.
Pitchstone - Natural glass | Britannica