BETH YW'R CERRIG NATURIOL MEDDALACH A LLE GELLIR EU DEFNYDDIO? carreg tirwedd

Pam fod rhai cerrig naturiol considered to be soft when they all appear to be hard? The answer lies within ‘relative’ hardness. Mohs scale of hardness was invented in 1812 and compares the relative hardness of ten minerals. Diamond is the hardest and rates a 10, while granite is the toughest natural stone at 6. Limestone comes in at 3 as does its metamorphic counterpart, marble. Softer stone is easier to dress or carve but does not wear or weather quite as well as harder stone. Here we discuss some of the more popular soft stones along with suitable applications.

Cerrig afreolaidd

Craig waddod

Calchfaen, tywodfaen a siâl yw'r mathau mwyaf cyffredin o graig waddodol. Ffurfiwyd y rhain trwy bwysau aruthrol, dros filiynau o flynyddoedd, gan leihau'r gwaddodion a oedd wedi disgyn i wely'r cefnfor.

Llechen

The layers in slate are described as being “foliated” and they are easily split apart to create whatever thickness is required. UK slate is considered to be hard and was traditionally used as roofing, while soft slate is found in China, Spain, Italy and the USA. With a broad range of natural slate colours, a multiple array of designs can be achieved, from contemporary to classic, rustic to refined. Slate is often recommended for high traffic areas, thanks to its remarkably durable composition. It is also non-porous and does not easily react with acid liquids. It is fire proof, weather resistant and achieves good slip resistance dues to its riven finish.

Calchfaen

Limestone is a very common building material and is formed mainly from the mineral calcite, derived from the calcium in bones and seashells deposited over the millennia and forced together through pressure. While it also contains magnesium, it is harder and more weather resistant, and can also be polished. Portland stone from the eponymous island in Dorset is probably the single most famous type of limestone and was used to build many of London’s great buildings. It is used for external cladding as well as paving, fireplaces and other internal and external decorative features. Its soft colours are its trademark visual attributes.

Tywodfaen

Mae'n debyg mai Tywodfaen oedd y garreg adeiladu a ddefnyddiwyd amlaf cyn 1800, ar gyfer popeth o bontydd i adeiladau urddasol. Fel y gellir casglu o'i enw, fe'i ffurfiwyd pan gafodd tywod, deunydd organig, calsit ac amrywiaeth o fwynau eraill eu hasio gyda'i gilydd o dan bwysau anhygoel dros y milenia. Ar gael naill ai gyda gwead bras neu gain ac yn draddodiadol wedi'i gyflenwi mewn gorffeniad di-sglein. Yn bennaf hufen, coch neu lwyd yn y DU, mae ei liw yn dibynnu ar y mwynau ychwanegol sydd ynddo. Mae silica yn rhoi gwynder, tra bydd haearn yn rhoi arlliw coch-frownaidd. Ei brif feysydd cymhwyso yw waliau a lloriau, neu bafin allanol.

Marmor

Mae marmor yn deillio o galchfaen, a ffurfiwyd trwy fetamorffosis gwres a gwasgedd aruthrol dros filiynau o flynyddoedd. Er ei fod yn gymharol feddal o'i gymharu â cherrig eraill, mae marmor yn tueddu i sgleinio'n anhygoel o dda. Yn draddodiadol, defnyddir marmor mewn drysau ac mae'n helpu i greu gorffeniad pen uchel.