| Granite.
Granite is a hard coarse-grained rock that makes up a large part of every continent. It is classified as an igneous rock. It is thought to have been formed by the slow cooling and crystallisation of molten magma formed from rock that had melted approximately 30 kilometers below the continent's surface. The magma, then lighter than the surrounding rocks rose to the surface. |
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| Granite consists mainly of three minerals - quartz, alkali feldspar, and plagioclase feldspar. These minerals give the granite its distinctive white, pink or light grey colouring. The granite may also contain small amounts of dark brown, dark green or black minerals like hornblende and biotite mica. The grains of the minerals in granite are so large that they can be easily distinguished. |
| The interlocked minerals make granite
a strong durable rock capable of withstanding weathering for hundreds of
years. For this reason, granite has become one of the most commonly used
materials in both the construction and road building industries. You will
have often seen the crushed granite being used in concrete mixes along
with sand and cement, and being mixed with tar for road surfacing. Fortunately
this also means that the stone is available almost everywhere, and will
almost certainly be available near to you.
The stone medium required by the FlowGrow system is a widely available granite product crushed and screened by most quarries for use in road building operations. It is crushed and screened to limit the chip size to 9.5mm. In South Africa the stone is most often described as "nine and a half (9 1/2) roadstone". You may want to avoid shipping costs and purchase the stone from a builders merchant, or directly from a quarry near you. Often the quarry will wash or double wash this product before delivery to remove the dust and fine particles. This wash, while it is helpful, is not sufficient for the purposes of the hydroponics system, and the stone requires further washing by the user to remove all dust and fine particles. The FlowGrow system requires 120 liters (by volume) per tray. The density of the stone is approximately 1.4 kg per liter, or 1.4 ton per cubic meter, giving a per tray weight requirement of approximately 168 kg. It is recommended that if the stone is being purchased unwashed, that approximately 180 kg be purchased, to allow for the loss of dust and fine materials in the washing process, and to allow a little extra for spare. The stone medium will last a lifetime and will not need to be replaced. We can supply the correct stone washed and ready to use, and packed in eight x 22kg bags. If you are purchasing the stone locally, a 500g sample of the stone medium will be supplied with the FlowGrow system to help you get the right product. |