The sillimanite group consists of three minerals andalusite, kyanite and sillimanite, all with the same chemical composition but with different crystal structures and physical properties. Andalusite has a hardness of 7.5, sillimanite 6-7 and kyanite 5-7. . The chemical formula is normally written as Al2O3.SiO2 with a theoretical composition of 62.93% alumina and 37.07% silica.

PROUD NOTE: Sillimanite gave its name to the group mainly because a large portion of supply in the early years of the industry was sillimanite from INDIA.

3Al2SiO5 >>Al6Si2O13 + SiO2
(sillimanite) (mullite) (tridymite)

All of the sillimanite minerals convert to mullite (about 88%) and silica (about 12%) on calcining or heating at temperatures of 1250° to 1500°C. Each of the minerals converts at a different temperature, with kyanite needing the least heat and sillimanite the most.

Although the three minerals that make up the group have the same chemical composition, their physical properties are different. Most importantly, sillimanite and andalusite increase irreversibly in volume by only about 4% and 6% respectively on calcining. They can be used directly in refractories without calcining because the small volume increase can be accommodated by the users and can be beneficial.


Calcination (also referred to as calcining) is a thermal treatment process in presence of air or oxygen applied to ores and other solid materials to bring about a thermal decomposition, phase transition, or removal of a volatile fraction.The calcination process normally takes place at temperatures below the melting point of the product materials. Calcination is not the same process as roasting. In roasting, more complex gas–solid reactions take place between the furnace atmosphere and the solids.This process is commonly used to remove volatile substances in a material, to improve its electrical conductivity, or to remove water or certain impurities.


The sillimanite minerals decompose irreversibly to mullite when burnt at high temperatures (calcina-tion), according to the reaction:

3Al2SiO5 >>Al6Si2O13 + SiO2
(sillimanite) (mullite) (tridymite)

Since mullite is the mineral component that is sought after by the refractory industry, the sillimanite minerals could almost be regarded as ‘mullite ore’.

Sillimanite , which only expands by 4-7 volume % during mullitisation, have the advantage that they can be used in their raw state.

REFRACTORIES: Refractories are materials that remain physically and chemically stable at high temperatures under extreme conditions of heat and corrosion . Those derived from sillimanite minerals belong to the group of high-alumina refrac-tories, i.e. refractories exceeding 47.5% Al2O3.



1.The major end use of sillimanite minerals is in the iron and steel industries which consume 60% or more of the mullite refractories . They are used in critical areas of furnaces, steel degassing chambers, soaking pits and many types of auxiliary pouring and handling equipment.

2.The sec-ond most important application is as furnace linings in the non-ferrous metallurgical and glass industries as well as in ceramic and cement kilns.

3. Other uses, minor in volume terms, include foundry-mould facings, combustion chamber lin-ings, burner bodies, pyrometer tubes and welding rod coat-ings.

4. The manufacturing of refractory bricks and shapes.

5. As well as of mortars or cements

6. Ramming and gunning mix-tures and castables (refractory concretes) used in the con-struction of joint-free and self-supporting monolithic refrac-tory linings.


7.Raw and calci-nated minerals are utilised in the manufacture of high-ten-sion insulators and other electrical ceramics, ceramic tile body components, sanitary ware, ceramic honeycombs, blown aluminium-silicate high-temperature insulation, brake linings, glass melt additives, spinnable mullite fibres, grinding media and extrusion dies. Sillimanite minerals are also locally used to produce Si-Al alloys, metallic fibres and selected aluminium oxides.


We are ready to serve you indigenous as well as the imported coal. We mine and trade predominantly coal for Thermal Plants, Cement factories, Steel plants, Rolling mills,Paper mills and Brick kilns.

Whether you need spot pricing or a long-term contract, you can count on 7 WATTS.



Understanding the growing demand of STEAM and COKING COAL in India, we have tied up with various mines in Indonesia, South Africa, Chile, Australia and Mozambique to facilitate the end users in India.

STEAM/THERMAL COAL: Thermal coal is sometimes called steaming coal because it is burned for steam to run turbines to generate electricity either to public electricity grids or directly by industry consuming electrical power .More than half of the electricity generated in the world is by using coal as the primary fuel.

The function of the coal fired thermal power plant is to convert the energy available in the coal to electricity that we find in our home that powers our lights, computers, and sometimes, back into heat for our homes.

FSA WITH POWER PLANTS: As per the coal specification and requirements of the Power Plants we can provide various qualities of Indonesian, South African and Chilean coal on a CIF / CFR basis. By signing long term FSAs( Fuel Supply Agreements) we are committed to supply the quality and quantity on a regular basis.

COKING COAL: Coking coal, also known as metallurgical coal, is used to create coke, one of the key inputs for the production of steel.Coking coal is typical for its low volatile matter content with a high swelling index. Based on the coking properties the coking coal can be divided into two groups:

semi-soft coking coal (also known as SSCC)

hard coking coal (also known as HCC)

By having tie ups with renowned Coking coal miners in Australia and Mozambique we can provide SSCC and HCC to the end users on a CIF/ CFR basis.

NEWYORK BRANCH OFFICE: Understanding the demand of coal in other parts of the world our branch office in New york is providing access to American Coal( lignite, thermal, anthracite) to interested clientele across the globe.



Coal plays a pivotal role in sustainable development. It is the most widely used energy source for electricity generation and an essential input to most steel production. As estimated by the World Coal Association, coal currently fuels 41% of the world electricity and this proportion is set to remain static over the next 30 years. About 70% of the world's steel production is based on coal. As per Integrated Energy Policy Committee of Planning Commission, coal will remain India's most important energy source till 2031-32 and possibly beyond. In India, about 77% coal output is consumed in power sector. In addition, other industries like cement, fertilizer, chemical, paper and thousands of medium and small-scale industries are dependent on coal for their process and energy requirements. The production of coal at 532.04 million tonnes in 2009-10 increased marginally to 532.69 million tonnes in 2010-11. The production of lignite at 37.73 million tonnes in 2010-11 increased by 10.75% from 34.07 million tonnes in the previous year. India ranks 3rd in world coal production (Ref: Indian Mineral Year Book 2011).

The Indian coal deposits are primarily concentrated in the Gondwana sediments occurring mainly in the eastern and central parts of Peninsular India, although Gondwana coal deposits also occur in Assam and Sikkim in north eastern part of the country. The Tertiary coal-bearing sediments are found in Assam, Arunachal Pradesh, Nagaland and Meghalaya. As a result of exploration carried out by GSI, CMPDI and other agencies, 285.86 billion tonnes (including that estimated in Sikkim) coal resources to 1,200 m depth have been established in the country as on 1.4.2011. Out of these resources, 114 billion tonnes were proved reserves, 137.47 billion tonnes were indicated reserves and the remaining 34.39 billion tonnes were in inferred category. Of the total resources, prime-coking coal was 5.31 billion tonnes, medium-coking & semi-coking were 28.16 billion tonnes and non-coking coal including high sulphur was 252.39 billion tonnes. Statewise/coalfield-wise and statewise/typewise reserves of coal as on 1.4.2011 are given in Tables-1 & 2, respectively (Ref: Indian Mineral Year Book 2011).


Meghalaya Coal has not been graded by Coal Controller. It is normally considered as non-coking Coal. Till recently, when coal was extracted only from the Eastern part of Meghalaya especially Jaintia Hills District, Meghalaya coal was considered to be a high Sulfur Coal. But the same is not true for the other parts of the state. For instances, West Khasi Hills Coal has lesser Sulfur content and Garo Hills Coal has the least. So the Graph of Sulfur content in Meghalaya Coal drops as we move from the Eastern Coal mines towards the West.

Meghalaya contributes about 1% of total coal production in the country and about 4% in value in terms of revenue or value in the whole country.


Gearing up for the tough and competitive times ahead, as the import of Coal from several coal exporting countries is made open into this country, 7Watts immediately put its professional team together and developed a new system of trading where prior to supply of coal to any buyers, the sample is first tested and chemically analyzed.

In this system various qualities and grades of coal is offered to buyers, for instances coal from Jaintia Hills, the extreme east of Meghalaya, West Khasi Hills and Garo Hills the extreme west of Meghalaya supported by a certificate. Because of our well established infrastructure in these different coalfields, we are able to offer critical logistics support. We ensure the timely delivery of the quantity and quality of coal from mine pit to the destination by means of road and railway rakes.

With the strength of our self owned and financed mines in Meghalaya and Nagaland we can supply good quantities of the following coal:


With an impressive track record of growth and performance, our strength includes a team of highly experienced professionals, a sophisticated fleet of earth moving and mining equipment with a superior material handling capacity and an ever-increasing distinguished clientele.