Portuguese ornamental limestones – [part 3]

3. GENERAL FEATURES OF THE TYPES OF LIMESTONES QUARRIED
Rocks classified as limestones, that have been referred to here, although chemically similar to those classified as marbles and in which the most common fundamental component is also the mineral calcite, are distinguished from the later ones in genetic and textural terms. In fact, while limestones
are sedimentary rocks composed of clastic elements held together by a calcitic and/or dolomitic cement (then called dolomitic or dolomite limestones depending on the percentage of dolomite mineral), marbles are the result of metamorphic action on limestones and are composed mainly of neoformed calcite.

In this group of limestones are those of clastic origin composed of fine or rough elements bound together by a carbonated cement (calciclastic and bioclastic limestones). Included in particular are the hard limestones, sometimes spathized, in which the structure of some elements is preserved, being usually an important aesthetic attribute. Also included in this classification are the biogenic and organic limestones (e.g. coraligenous limestones, spines of Echinodermata, etc.), and certain types of sedimentary rock originated from chemical precipitation (alabasters, etc.) formed by well crystallised calcite or aragonite although not affected by any metamorphic process. It is important to point out that these are sedimentary rocks and not marbles as, wrongly, many limestone producers throughout the world call them, because the petrographic classification of marble implies complete recrystallisation of carbonates and the neoformation of minerals, brought about in the metamorphic process.

Maciço Calcário Estremenho limestones:
Azul Molianos
Azul Valverde
Banco de baixo
Banco do fundo
Branco do Mar
Brecha Portuguesa
Brecha de S.to António
Moca Creme

Molianos macio
Molianos rijo
Olho de Sapo
Relvinha

Rosado de Ansião
Semi-rijo
Semi-rijo do Codaçal
Topázio
Vidraço de Ataíja creme
Vidraço de Ataíja azul
Vidraço de Moleanos

Region to the North of Lisbon limestones:

Amarelo de Negrais
Cinzento-Azulado
Encamadão
Encamadão “Chainette”
Encamadão de Lameiras
Encarnado da Pedra Furada
Lioz
Lioz Azulino
Lioz de Montemor

St Florient Rose

Algarve basin area limestones:
Brecha Acinzentada
Brecha Avermelhada
Brecha Pérola

4. CONCLUSIONS
The Portuguese industry of ornamental limestones has increased significantly over the past 20 years, which has much to do with intense quarrying in the Maciço Calcário Estremenho. Bearing in mind current producing centres, Portugal’s potential is good in this sector. Contributing to this potential are the large areas of outcrops potentially favourable to quarrying ornamental limestones in the units of Moleanos and Codaçal (Maciço Calcário Estremenho) and the Serra de Sicó. To correctly assess and evaluate this potential, more detailed geological surveys are required. These will help outline new target areas, as well as establish the criteria for rational quarrying, taking into consideration environmental and landscape values so that the well being of local populations is not
affected.

This sector of the industry is well skilled with exploitation and transformation units incorporating the most modern technologies. Thus assures its competitiveness and the generation of important profits, useful to the regional development and the national economy.

Author: Jorge Carvalho, Giuseppe Manuppella and A. Casal Moura (Geologists of the Instituto Geológico e Mineiro – Portugal)
Source: Rochas & Equipamentos