Andesite is an extrusive igneous rock that occurs due to cooling process of intermediate-basalt magma on earth surface. Generally, it has afanitic to porphyritic texture, grey to greyish black color, the density is 2.3 to 2.7, compressive strength ranging from 600 kg/cm2 to 2.400 kg/cm2. It could appear as crack, sill, lava-flow or as a component on volcanic lava. Andesite is used primarily for construction raw materials (aggregate) and ornamental stone.
Andesite quarry is generally done by open pit mining. It can utilize simple or heavy-tools equipment, depends on the mine production capacity. For a medium or high scale mining, it involved drilling and blasting process, since the hardness of andesite. The andesite mining stage consist of; soil cover stripping, extraction (manually or by drilling), loading and transporting to further processing location. Depending on the necessity, sometimes its size has to be reduced with tools (crusher) for road foundation utilization.
Occurrences
In several provinces in Indonesia, andesite is found on lava-boulder, lava and intrusion that formed on steep rugged hills. Petrographic analysis shows mineral composition such as plagioclase, pyroxene, hornblende, biotite, quartz, opaque, sericite, chlorite and clays with varying percentages.
Figure Andesite in Ndone District, Ende Regency,
East Nusa Tenggara Province
Resources
Based on Non-Metallic Mineral Resources, the potential andesite resources are located in 376 locations spread over 28 provinces in Indonesia. Indonesian andesite total resources are 84,298 million tons. The details can be seen in the table below. The percentage of andesite resources in each province in Indonesia is shown in the figure below.
Table Andesite in Several Provinces
Based on data from the Indonesia Statistics Agency (BPS) in 2015 as shown in the figure below, andesite production volume shows a decreasing trend from 2012 to 2015. Andesite production volume decreases from 15,614,556 m3 in 2012 to 7,294,371 m3 in 2015.
The decreases of andesite production were caused by the improvement of construction concrete that serves as a substitute for building and road foundation. For some big cities in general, they already use concrete as foundation in construction material because it is considered more economical and efficient in execution.
However, since 2015, infrastructure development has become a national priority, so the use of Andesite as raw material is expected to increase.
Figure Andesite Resources in each Province
Figure Andesite Production Volume on 2011-2015 (Indonesia, Statistics 2015)
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