Sulphur is considered a secondary element, along with calcium and

magnesium. Sulphur is required in moderate

amounts by pants, but is less likely to limit crop growth than nitrogen,

phosphorus or potassium.Sulphur has been known from ancient times. The ancient Indians, the Inca Indians, Greeks and Romans used

sulphur, as a fumigant, and in certain medicines.

The word "Sulphur" is probably derived from the Sanskrit word "Sulveri"

meaning "enemy of copper" as copper loses all its properties when heated with

sulphur. It has been mentioned in the Bible on many occasions, as

"Brimstone".

   

In the free state, sulphur is found in areas that have had volcanic activities.It is mostly found in Sicily in Italy

and in Texas and Louisiana in the USA. To a lesser extent it is found in Russia,

Canada, Japan and Poland. In the combined state, it exists as sulphide, sulphates etc.

The following are the chief sulphur-minerals. Galena (PbS)

Zinc blende (ZnS)Cinnabar(HgS)

Iron pyrites (FeS2)Gypsum (CaSO4.2H2O) 

Galena is a common and popular mineral for rock hounds.

Its characteristic cubes, distinctive cleavage and high density

make it easy to identify and a favorite in high school geology labs. The structure of Galena is identical

to that of halite, NaCl. The two minerals have the same

crystal shapes, symmetry and cleavage.

Some Galena may contain up to 1% silver in place of lead.

The large volume of Galena that is processed for lead produces

enough Silver as a by product to make Galena the leading ore of

Silver.

Chemistry: PbS, Lead Sulfide

Class: Sulfides Group: Galena

Uses: Major ore of lead and silver

Zinc sulfide (or zinc sulphide) is a chemical compound with the formula ZnS. Zinc sulfide is a white to yellow colored

powder or crystal. It is typically encountered in the more stable cubic

form, known also as the mineral sphalerite. The hexagonal form is also

known both as a synthetic material and as the mineral wurtzite. Both sphalerite

and wurtzite are intrinsic, wide-bandgap semiconductors. The cubic form has a

band gap of 3.54 eV at 300 K whereas the hexagonal form has a band gap of 3.91

eV.A transition from the sphalerite form to

the wurtzite form occurs at around 1293.15 K. Sphalerite melts at 1991 K. It has a standard enthalpy of formation of

−204.6 kJ mol−1 at 298 K.

Cinnabar is a colorful mineral that adds a unique color to the mineral color palette. Its cinnamon to scarlet red color can be very attractive. Well shaped crystals are uncommon and the twinned crystals are

considered classics among collectors. The twinning in cinnabar is distinctive and

forms a penetration twin that is ridged with six ridges surrounding the point of a

pryamid. It could be thought of as two scalahedral crystals grown together with

one crystal going the opposite way of the other crystal. Cinnabar was mined by the Roman Empire for its mercury content

and it has been the main ore of mercury throughout the centuries.

Chemistry: HgS, Mercury Sulfide

Class: Sulfides and Sulfosalts

Uses: primary ore of mercury, a pigment and as a

minerals specimen.

Pyrite is the classic "Fool's Gold". There are other shiny brassy yellow minerals, but pyrite is by far the most common and the most often mistaken for gold.

Whether it is the golden look or something else, pyrite is a favorite

among rock collectors. It can have a beautiful luster and interesting crystals. It is so common in the earth's crust that

it is found in almost every possible environment, hence it has a vast number of forms and varieties.

Chemistry: FeS2, Iron Sulfide Class: Sulfides Group: Pyrite

Uses: A very minor ore of sulfur for sulfuric acid, used in jewelry under the trade name

"marcasite" and as mineral specimens.

Chemistry: CaSO4-2(H2O), Hydrated Calcium Sulfate

Class: Sulfates Uses: plaster, wall board, some cements, fertilizer, paint filler,

ornamental stone, etc..

Gypsum is one of the more common minerals in sedimentary environments. It is a major rock forming mineral that produces massive beds, usually from precipitation out of highly saline waters. Since it forms easily from saline water, gypsum can have many inclusions of other minerals and even trapped bubbles of air and water.

 Herman Frasch in 1894 devised a brilliant technique of obtaining sulphur from these deposits. In this process, now called the Frasch process, a system of three concentric pipes is sunk into the earth to reach the sulphur beds (about 300m deep).Outer pipeIn this pipe, superheated water (170oC) is sent down under 10 atm pressure. This melts the sulphur in the beds of the soil.Inner most pipeHot compressed air is simultaneously blown down this pipe, which causes the frothing of sulphur.Middle pipe The simultaneous pressure of air in the inner pipe and water of the outermost pipe forces the sulphur froth to rise up

Impure sulphur is heated in an iron retort. The sulphur vapors formed at 444oC are allowed to escape in a large brick chamber. The vapors condense and form 'flowers of sulphur' on the walls of the chamber. After sometime when the temperature of the chamber rises up to 120oC, these flowers of sulphur melt and collect at the bottom of the chamber. The molten sulphur is poured into cylindrical moulds and allowed to solidify. Sulphur so obtained is called roll sulphur.

Large quantities of hydrogen sulphide are obtained from the purification of petroleum gases along with other gases such as methane and carbondioxide. These gases are removed and hydrogen sulphide is oxidised to sulphur in different stages using heated bauxite as catalyst.

Rhombic Sulphur (Octahedral or Alpha Sulphur)

Rhombic sulphur is prepared by dissolving roll sulphur in carbon disulphide, and then evaporating the solution slowly, at room temperature. Eight sided crystals of rhombic sulphur crystallizes outRhombic or octahedral sulphur consists of rings of 8 atoms of sulphur. It is the most stable of all the allotropes of sulphur. It is soluble in carbon disulphide, benzene, chloroform, etc., but is insoluble in water. It is non-conductor of heat and electricity. It is transparent and pale yellow in color.

Monoclinic Sulphur (Prismatic or Beta Sulphur)

This allotrope of sulphur is prepared by melting roll sulphur in a dish. The molten sulphur is allowed to cool slowly. The top layer solidifies first and forms a crust. Two holes are made in the crust with the help of a heated nail. The molten sulphur is poured out through one of the holes. Then with the help of a knife the crust is carefully peeled off. Pale-yellow, transparent needle shaped crystals are seen projecting out form the inner surface of the dish. These are the crystals of monoclinic sulphur. Monoclinic sulphur also consists of 8 atom rings. It is stable only above 96oC. When it cools down below 96oC, it changes to rhombic sulphur i.e., 96oC is the transition temperature of this sulphur.

Milk of sulphur is prepared by the action of dilute hydrochloric acid on ammonium sulphide. Milk of sulphur is also prepared by boiling roll sulphur with an aqueous solution of calcium hydroxide. The mixture is then filtered and dilute hydrochloric acid is added to the filtrate to get milk of sulphur. Milk of sulphur is non-crystalline and white in color. It is soluble in carbon disulphide. When heated it changes to the ordinary yellow variety of sulphur. It is used in medicine.

 

On heating sulphur, till almost the boiling point and suddenly cooling it by pouring into cold water a viscous mass is formed. This sudden cooling does not allow sufficient time to the molecules to rearrange themselves to form monoclinic or rhombic forms of sulphur. Hence the molecules form an interwined mass, consisting of both rhombic and monoclinic varieties of sulphur. This is called plastic sulphur

 This type of sulphur is a dark brown or even black, sticky substance. It is elastic. It has no sharp melting point. It does not dissolve in carbon disulphide. On standing, it slowly changes to the rhombic forms, as it gains the eight atom ring structure.

 

When heated, sulphur undergoes a series of characteristic changes.

Sulphur can melt at two different temperatures.

a) If heated rapidly, it melts at 112.8oC.b) But if heated slowly it will melt only at

118.6oC.As a result the liquid is quite mobile. As the color gradually darkens form pale yellow to

amber color At 160oC, it becomes so viscous that it looks almost tar-like, and it does not

flow out even if the test tube is inverted .When heating continues the liquid

once again becomes mobile .At 444oC, sulphur begins to boil giving off light

yellowish orange vapors. When the vapor are cooled, they solidify to form a Yellow

powder of flowers of sulphur.

We find many sulphur compounds on Earth. These include sulphur dioxide, elemental sulphur, sulphuric acid, salts of sulphate or organic sulphur compounds such as dimethylsulphide and even amino acids in our body.  All these chemical compounds do not last forever. They are transported by physical processes like wind or erosion by water, by geological events like volcano eruptions or by biological activity. They are also transformed by chemical reactions. But nothing is lost. Changes often take place in cycles. Such cycles can be chemical cycles in which a sulphur compound A reacts to form B, B to C, C to D and D to A again. One example is when sulphur compounds move from the ocean to the atmosphere, are transported to the land, come down with the rain and are transported by rivers to the ocean again.