Generally vents are hot, acidic environments. The thermal energy comes from two main sources. The first main source is the earth, more specifically, the mantle beneath the crust. The second main source of thermal energy is the exothermic chemical reactions that take place at the vent site. The acidity comes from the large amount of hydrogen sulfide produced. Here are a couple of examples of reactions that occur at the vent site, which make the water more acidic:

Fe2+ + H2S à FeS + 2H+
Cu2+ + H2S à CuS + 2H+

Another common compound found at the vent site is a white solid called calcium sulfate. It is produced by the following reaction:

Ca2+ + SO42- à CaSO4

The reason that black smokers are black is the precipitation of the black colored compound, iron sulfide (FeS2), better known as fool's gold.

The typical chemical content of the hydrothermal vent fluids is as follows:
100 ppm Fe } measurements in ordinary seawater
Few ppm Zn, Cu, Ni } is measured in parts per trillion
210 ppm H2S
1290 ppm silica
No Mg or SO42- in solution

Seafloor hydrothermal activity at mid-ocean ridges influences The chemistry of oceans Extensive alteration of oceanic crust

Most ridge crust systems form hydrothermal fluid from high temperature chemical reactions between seawater and oceanic crust.

This hydrothermal fluid is often
-Acidic
-Reducing
-Sulfur rich
-Metal rich

Large differences in processes among vents account for the wide variety of chemistry from vent to vent. The Edmond Vent System's chemical composition has not yet been documented

Extensive biological diversity can be sustained if the diffuse flow contains
-Amorphous Iron-oxyhydroxides
-Amorphous Manganese-oxides
- Authigenic clays
-Silica

Clusters of tubeworms are typically anchored to the sea floor by solid deposits of
-Iron oxides
-Silica
-Barite
-Marcasite

Two major constituents of white smokers are
- Amorphous silica SiO2
-Barite BaSO4

Most chimney structures can be typified with sharp thermal and chemical gradients The walls of the vent exhibit semi thermal insulation, which allow for deposit of
- Pyrite-marcasite (FeS2)
- Sphalerite (ZnS)
-The walls are porous so the cold seawater can mix

Black smoker vents can be differentiated from chimney vents by
-Chalcopyrite lines orifice
-Anhydrite-rich wall

Typical materials found in black smokers
-Copper and Iron sulfides
-Various crystal structures of Chalcopyrite
-Isocubinite (a quenched high temperature copper-iron sulfide solid solution)
-Pyrrhotite (nonmagnetic hexagonal form)

Rare compounds found in black smokers
-Magnesium silicates
-Lizardite
-Stevensite
-Magnesium hydroxysulfates
-Caminite
-Starkeyite
-Apatite with iron magnesium silicates

Black smoker fluids are also buffered to near equilibrium with
-Pyrite
-Pyrrhotite
-Magnetite
-High concentrations of reduced compounds
-Ferrous iron
- Hydrogen sulfide

The deposition of chalcopyrite is a function of
- Decreasing Temperature
- Increasing pH

Typical Elemental constituents of ocean floor sulfide deposits near the vent system
- Copper and iron sulfides
- Cobalt
- Selenium
- Molybdenum
- Zinc sulfides
- Arsenic
- Antimony
- Lead
- Cadmium
- Silver
- Gold

The solubility's of metals in aqueous chloride complexes has an order of magnitude that is several orders of magnitude larger than of normal seawater.

Major sources of copper, iron and zinc are
-Dissolution of immiscible sulfides
-Destruction of ferromagnesian minerals

Lead and Barium are mainly derived from the destruction of feldspars