Sandstone
Sandstone is a clastic sedimentary rock comprised mainly of sand particles. The size of the particles can be subdivided into very fine (0.0625 to 0.125mm), fine (0.125 to 0.25 mm), medium (0.25 to 0.50 mm), coarse (0.50 to 1.00 mm), and very Coarse (1.00 to 2.00 mm).
Clastic is defined as rock made up of broken pieces of older rocks. Sandstones are further categorised on the basis of their grain types, which can be quartz, feldspar or rock fragments (lithic).
Sandstones are deposited by a wide variety of processes, such as fluvial (river), alluvial (river), aeolian (wind) and turbidity currents (underwater currents). Like sand, sandstone may be any colour, but the most common colours are: tan, brown, yellow, red, grey, pink, white and black.
Quartz Sandstone
Quartz sandstone results from extreme weathering and sorting of a sediment until everything possible to remove has been removed. Removal of feldspar and lithic particles results in the high content of quartz. This is achieved by complete chemical weathering.
Weathering
Although quartz sandstones are not especially susceptible to solution damage from acid rain, they are quite prone to physical disruption by salts, which crystallise within their pores. These are often a combination of marine salts such as sodium chloride, complex salts contained within rising groundwater and pollution derived salts, particularly calcium sulphate (gypsum).
When salts crystallise within the stone, repetition of expansion and contraction can lead to features such as granular disaggregation (separation of grains), scaling and multiple flaking.
In areas that are sheltered from rainwash, accumulations of gypsum on the surface can incorporate soot particles to form unsightly and potentially damaging black crusts. Over time, moisture movement corrodes metal fixings that can expand and fracture the stone.
Moisture also mobilises iron from within the stone and concentrates it at the surface. This forms a hard crust, but if this is breached, the stone behind is rapidly hollowed out to form honeycombs and larger cavernous hollows.
The sandstone detailing of the Lanyon Building shows a wide range of salt related decay phenomena including blisters, scaling and granular disaggregation, which disfigures statues and carved details, and is hollowing out many flat surfaces.
To log this earthcache as a find, please send me answers to the following questions via my profile:
1. What type of rock is sandstone: metamorphic, igneous or sedimentary?
2. The entire building is not made of sandstone. Where can you see that sandstone has been used?
3. Down low on either side of the main entrance, there are two gargoyles: what has weathering done to these?
4. Based on the information provided above and your observations, what type of weathering was at work here?
OPTIONAL: Attach a photo of you/your GPSr/smartphone with the building (without including any spoilers).
You do not have to wait for my response to log your find. I will contact you in case of any issues.
Happy Earthcaching!
| I have earned GSA's highest level: |
 |