Carbonate Petrography

Carbonate petrography is the study of limestones, dolomites and associated deposits under optical or electron microscopes greatly enhances field studies or core observations and can provide a frame of reference for geochemical studies.

25 strangest Geologic Formations on Earth

The strangest formations on Earth.

What causes Earthquake?

Of these various reasons, faulting related to plate movements is by far the most significant. In other words, most earthquakes are due to slip on faults.

The Geologic Column

As stated earlier, no one locality on Earth provides a complete record of our planet’s history, because stratigraphic columns can contain unconformities. But by correlating rocks from locality to locality at millions of places around the world, geologists have pieced together a composite stratigraphic column, called the geologic column, that represents the entirety of Earth history.

Folds and Foliations

Geometry of Folds Imagine a carpet lying flat on the floor. Push on one end of the carpet, and it will wrinkle or contort into a series of wavelike curves. Stresses developed during mountain building can similarly warp or bend bedding and foliation (or other planar features) in rock. The result a curve in the shape of a rock layer is called a fold.

Pearl gemstone

What is Pearl Gemstone?

A pearl is a hard object produced within the soft tissue (specifically the mantle) of a living shelled mollusk. Just like the shell of a clam, a pearl is composed of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other shapes (baroque pearls) occur. The finest quality natural pearls have been highly valued as gemstones and objects of beauty for many centuries. Because of this, pearl has become a metaphor for something rare, fine, admirable and valuable.
The most valuable pearls occur spontaneously in the wild, but are extremely rare. These wild pearls are referred to as natural pearls. Cultured or farmed pearls from pearl oysters and freshwater mussels make up the majority of those currently sold. Imitation pearls are also widely sold in inexpensive jewellery, but the quality of their iridescence is usually very poor and is easily distinguished from that of genuine pearls. Pearls have been harvested and cultivated primarily for use in jewellery, but in the past were also used to adorn clothing. They have also been crushed and used in cosmetics, medicines and paint formulations.
Whether wild or cultured, gem-quality pearls are almost always nacreous and iridescent, like the interior of the shell that produces them. However, almost all species of shelled mollusks are capable of producing pearls (technically "calcareous concretions") of lesser shine or less spherical shape.

History and Introduction

Pearls are organic gemstones that are formed by shelled molluscs; mainly bivalved oysters and mussels. Pearls are made up of nacre (mother-of-pearl) which is mostly aragonite (calcium carbonate) and conchiolin (complex proteins that form mollusc shells). The aragonite microcrystals build up around an irritant. The name "pearl" is said to have originated from the Middle English word "perle", which in turn came from the Latin word "perna", meaning "leg", thought to be due to the ham-leg shape of the bivalve mollusc.
Natural pearls are extremely rare, incredibly expensive and typically small. Therefore people have developed ways to culture pearls, so that these beautiful gemstones can be enjoyed by many. In cultured pearls, some tissue or a mother-of-pearl bead is introduced into the mollusc shell. If successful, this process induces the animal to form a "pearl sac" whose cells secrete a layer of brownish protein called conchiolin over the irritant. This is followed by the secretion of numerous mineral layers of nacre composed of calcium carbonate in thin overlapping plates. Pearls can come from fresh or seawater molluscs. The beauty of pearls is that they can be plucked from the shell naturally beautiful, fully-formed and displaying perfect lustre with no need to be cut or polished.
The oldest recorded reference to pearls in history is the 7,500 year-old "Umm Al Quwain Pearl", which was found in a grave in a place that is now known as the UAE. Before pearls were cultured by man, they were harvested from the Persian Gulf, Sri Lankan waters, fresh water sources in China and the rivers of Europe. Later, Christopher Columbus discovered pearls in South America. When these natural pearls were almost depleted in the early twentieth century, the Chinese and Japanese began to culture pearls and the rest is history. Nowadays, pearls remain a treasured adornment and are cultured all around the world.

Physical properties

The unique luster of pearls depends upon the reflection, refraction, and diffraction of light from the translucent layers. The thinner and more numerous the layers in the pearl, the finer the luster. The iridescence that pearls display is caused by the overlapping of successive layers, which breaks up light falling on the surface. In addition, pearls (especially cultured freshwater pearls) can be dyed yellow, green, blue, brown, pink, purple, or black. The very best pearls have a metallic mirror-like luster.
Because pearls are made primarily of calcium carbonate, they can be dissolved in vinegar. Calcium carbonate is susceptible to even a weak acid solution because the crystals of calcium carbonate react with the acetic acid in the vinegar to form calcium acetate and carbon dioxide.

Identifying Pearl

Pearls can be identified by their pearly lustre and when rubbed gently against the teeth, a slightly rough surface texture can be detected, whereas imitation pearls feel smooth. The surface appearance of natural and cultured pearls is the same, but the density of cultured pearls is usually higher, at approximately 2.73 for most. The only definite way of distinguishing between natural and cultured pearls is to examine their internal structure. Experts use endoscopes to do this through the drill holes of pearls. Natural pearls have concentric internal layers.

Pearl: Origin and Gemstone Sources

Pearls are found and cultured in waters all over the world. Natural sea pearls are found in Australia, Japan, Central America, the Persian Gulf, the Gulf of Manaar (between India and Sri Lanka), the coast of Madagascar, Burma (Myanmar), the Philippines, the South Pacific Islands (including Tahiti and Fiji) and South America.
Natural river pearls are found in Asia, Europe and North America.
Cultured seawater pearl sources include Southeast Asia (such as Indonesia and the Philippines), Australia, China, French Polynesia, Japan, South Pacific Islands (including Tahiti and Fiji) and the Philippines.
Cultured freshwater pearl sources include China and Japan.
Basra pearls where basra moti in the Indian language, natural pearl gemstone which are found in the Indian Ocean are also called as basra pearls.

Freshwater and saltwater pearls

Freshwater and saltwater pearls may sometimes look quite similar, but they come from different sources.
Freshwater pearls form in various species of freshwater mussels, family Unionidae, which live in lakes, rivers, ponds and other bodies of fresh water. These freshwater pearl mussels occur not only in hotter climates, but also in colder more temperate areas such as Scotland (where they are protected under law). Most freshwater cultured pearls sold today come from China.
Saltwater pearls grow within pearl oysters, family Pteriidae, which live in oceans. Saltwater pearl oysters are usually cultivated in protected lagoons or volcanic atolls.

Determining Pearl Gemstone Value

Pearl Colour

Pearls are available in a variety of colours. Colours of pearls include the following: White, pink, silver, cream, golden, green, blue and black. Some pearls exhibit iridescence, which is known as orient.

Pearl Clarity and Lustre

The lustre of pearls depends on the quality of the nacre. Pearls should have the characteristic shiny pearly lustre and their surface should show sharp and bright reflections. The surfaces of good quality pearls are smooth and blemish-free with a suitable layer of nacre to increase durability.

Pearl Cut and Shape

Pearls can be round, oval, pear-shaped or misshapen (baroque pearls). However, the best materials are regularly shaped. The most valuable shapes are symmetrical spheres or symmetrical drops. Pearl sizes depend on the type of mollusc that they form in and they typically range from 2 mm to 16 mm in diameter.

Pearl Treatment

Pearls are often bleached to lighten and enhance their colour. In this way, a uniform colour can be achieved for beaded necklaces.

Metaphysical properties of Pearls

Pearls symbolise Purity, Spiritual Transformation, Charity, Honesty, Wisdom and Integrity, all the best within us. Pearls provide a clear vehicle for the advancing states of wisdom, as well as a clean channel for receipt of spiritual guidance.
Pearls can stimulate your femininity and help with self acceptance. They lift your spirits and make you feel calm and beautiful. They remind us to walk with Dignity.
Pearls not only provide a mirror in which to see ourselves, but give us insight into how we appear to others.
The ragged, rough grain of sand, transformed over time slowly growing into a object of great value and beauty. With it's humble beginnings, Pearls symbolise innocence and a pure heart, and help us get in touch with the simple honest things of life.
Pearl grants to its wearer extraordinary foresight, protects him from risky commercial transactions and from evil eye. Pearl's magical properties depend on its colour: white Pearl brings freedom, brownish - wisdom, yellowish - wealth, greenish - happiness.
Pearl signifies faith, charity and innocence. It enhances personal integrity and helps to provide a focus to ones attention. Pearl symbolises purity and is known as a “stone of sincerity”. It brings truth to situations and loyalty to a “cause”. Inhibits boisterous behaviour.

Healing properties of Pearls

Pearls have been used throughout medical history to help treat disorders of the digestive tract, muscular systems and the skin. Powders and potions containing pearls have also been developed to aid in fertility, as well as in easing the discomforts of the birthing process. Many cultures and societies have made similar claims for this lustrous gem.
The Chinese, for example, have depended on the healing properties of the pearl for centuries. They have used it to treat everything from simple eye ailments to serious heart problems, bleeding, fever and indigestion. To this day, the Chinese still use pearl powder as a skin whitener and a cosmetic, as do many other people around the world. In fact, the pearl is widely considered to be effective in controlling the skin conditions rosacea and acne.
Pearls are considered to be very effective in treating health issues related to the stomach, heart and spleen. It calms the mind and prevents hysteria, promoting mental stability.It was believed that Pearl boosts sexual energy, strengthens visual acuity and heals ears diseases. It is beneficial for heart, lungs (against tuberculosis, asthma, chronic bronchitis), kidneys, urinary system and liver. Pearl possesses sedative and also laxative effect, neutralises poison, lowers acidity, It relieves conditions of bloating and biliousness.
Pearl increases fertility and eases childbirth. Pearl also raises sensuality. Pearl was believed to be the main ingredient of "immortality elixir".

Properties of Pearl gemstone

ColourWhite, Blue, Green, Yellow, Orange, Brown, Pink, Purple, Gray, Black, Multicolored
Hardness2.5 - 4.5
Crystal SystemAmorphous
Refractive Index1.52 - 1.69
SG2.6 - 2.8
TransparencyOpaque
Double Refraction.156
LusterPearly
CleavageNone
Mineral ClassCalcium carbonate and conchiolin (organic) combined with water

Orthoclase gemstone

What is Orthoclase gemstone?

Orthoclase is a mineral that belongs to the family of silicate minerals called feldspar. The deference between the feldspars and the other silicates is that the former contain a mixture of the following chemical elements: Potassium K, Calcium Ca and Sodium Na, in addition to the usual constituents of the quartz based minerals, such as Aluminium, Al, silicon Si and oxygen O. 
The other related crystals from this family are the attractive labradorite, moonstone, sunstone, and amazonite. Orthoclase crystal, as its name already indicates, is a member of the orthoclase feldspars, The most important feature of this class is that they contain K and Na, in contrast to Ca and Na contained in the plagioclase.
A typical orthoclase is a solid solution of KAlSi3O8 and albite NaAlSi3O8. The origin of its name is probably from the Greek name for e or transparent. The golden variation can be found on Madagascar and in Mexico. The other colours are more frequent. If of gemstone quality orthoclase resembles golden or yellow beryl, also known as heliodor
Orthoclase an important mineral for industrial applications. Amongst the other uses, it is a source material for porcelain production. Porcelain (the vitrified ceramic of white colour) is produced from a mixture of orthoclase, quartz and kaolin.

History and Introduction

Orthoclase is a rare gemstone that belongs to the feldspar group, which also includes moonstone, amazonite, spectrolite and labradorite. Therefore, orthoclase is sometimes also called "K-spar". Orthoclase gemstones are typically champagne yellow, golden yellow or greenish, though they can be other colours. The name, "orthoclase" is a Greek word meaning "straight fracture", which refers to the cleavage planes of orthoclase being at right angles to each other. Orthoclase is faceted into attractive gemstones and also has an industrial use as a scouring agent in the making of some glasses and ceramics.

Identifying Orthoclase

Orthoclase is difficult to identify from other gemstones by appearance alone. It can be distinguished from similar gemstones by its hardness, low birefringence colours and perfect cleavage.

Orthoclase: Origin and Gemstone Sources

Orthoclase is found in Madagascar, Burma (Myanmar) and Kenya.

Determining Orthoclase Gemstone Value

Orthoclase Colour

Orthoclase is often colourless or champagne-coloured, but it can also be pink, green, orange or bluish. Gem quality materials are typically champagne, golden yellow or greenish.

Orthoclase Clarity and Lustre

Orthoclase is opaque to transparent and good quality specimens are eye clean. It has a vitreous lustre. Materials that display opalescence are classed as moonstone.

Orthoclase Cut and Shape

Transparent materials are faceted and opaque materials are usually cut en cabochon.

Orthoclase Treatment

Orthoclase is not currently known to be treated or enhanced in any way.

Orthoclase Healing properties

Orthoclase is a highly beneficial crystal for reversing the declining processes in our body. Not only that, it will help you prevent the fear of getting old and make you understand that the Spirit is always staying young no matter in what condition your physical body is. 
This crystal protects the internal organs, strengthens the bones, boosts our energy, and restores our will, therefore effectively buying us some time for a quality and happy old-age life.

Orthoclase metaphysical properties

In the new age community, the pleasant and refined energies of this metaphysical semi precious crystal are associated with hope, new beginnings, better perception, and discernment. It can be useful for revealing emotional tensions. It can be used for chakra balancing and meridian activation. This stone of cooperation and group work, encourages finding novel and unconventional paths toward achieving our goals. 
Besides being useful in joint ventures, this gemstone encourages inner growth and conducting constructive actions and carefully planned agendas. Primarily associated with the solar plexus chakra, it can enhance our will and knowledge as to how to improve our relationship to the Universe and Its powers.

Properties of Orthoclase

Chemical FormulaKAlSi3O8
ColourGreen, Yellow
Hardness6 - 6.5
Crystal SystemMonoclinic
Refractive Index1.52 - 1.53
SG2.56 - 2.59
TransparencyTransparent
Double Refraction-.008
LusterVitreous
Cleavage2,1 - basal ; 2,1 - prismatic ; 3,1 - pinacoidal
Mineral ClassSanidine

Different shale distributions in low resistivity log response.


                   First, we will start with a small introduction about the resistivity logs                                           

Resistivity log

Technique : produce a current in the adjacent formation and measure the response of the formation to that current.

Resistivity logs are used to:

• determine hydrocarbon-bearing versus water bearing zones
• indicate permeable zones
• determine porosity

By far the most important use of resistivity logs is the determination of hydrocarbon-bearing versus water-bearing zones. Because the rock’s matrix or grains are non-conductive and any hydrocarbons in the pores are also non-conductive, the ability of the rock to transmit a current is almost entirely a function of water in the pores. As the hydrocarbon saturation of the pores increases (as the water saturation decreases), the formation’s resistivity increases. As the salinity of the water in the pores decreases , the rock’s resistivity also increases.

Resistivity tools principle : there are two types of resistivity tool , The dual lateral log ( DLL ) and the induction log ( DIL ) both types measures the resistivity in three zones simultaneously.

LLD looks deep into reservoir

LLS Looks shallow into the reservoir


MSFL reads the resistivity close to the wellbore.




Low Resistivity response :

High deep resistivity means : HCs or Tight streak  { low porosity }

Low deep resistivity means : Shale or wet sand.



Shale: Shale is defined as a fine-grained, indurated detrital sedimentary rock formed by the consolidation (by compression or cementation) of clay, silt, or mud.
It is characterized by a finely stratified structure of laminae ranging from 0.1 to 0.4 mm thick. Shale contains an appreciable content of clay minerals or derivatives from clay minerals, with a high content of detrital quartz; containing at least 50% silt, with 35% clay or mica fraction, and 15% chemical or authigenic materials
In petrophysical analysis, shale volume is one of the key answers used later to correct porosity and water saturation for the effects of clay bound water, (CBW).


Shale distribution in shaly sand :
 
Shale can be distributed in several different ways, as shown below.

Laminated shale is a special case in petrophysical analysis. Standard models for porosity and saturation do not work.
Dispersed shale is usually composed of from clay minerals that form in place after deposition due to chemical reactions between the rock minerals and the chemicals in the formation water.
Structural shale is usually deposited as particles, grains, or clasts during the initial depositional phase. For example, the flooding of a river valley can carry mud or shale from surrounding areas.
Different shale distributions have different effect on the sand reservoir.
In a sand reservoir contain structure shale : it will affect the reservoir porosity
In a sand reservoir contain laminae shale : it will affect only the net pay of the reservoir

In a sand reservoir contain : it will affect the porosity and permeability of the reservoir and also it will lead to a shortcut in the resistivity log response , which may result in a miss lead in the interpretation of the reservoir porosity and saturation  , it could be interpreted as sand bearing water instead of a sand contain dispersed shale.
So, the question here is how to differentiate between them and to avoid this wrong interpretation ?!
Let’s assume that you have a 100% clean sand reservoir. So the total porosity of this reservoir is 30% and the sand grains will represent 70% of the volume of the reservoir
Hint : Porosity of sandstone is 30 % and porosity of shale is 10%

Case 1 :

In the case of the presence of structure shale ,
So in this case shale grains will replace sand grains ( volume of 70% ) , the shale will bring its 10% porosity with it.
In other words , The porosity will be enhanced by 10% in the volume of 70% of the sand
So , the porosity will increase by 70/10 and the total porosity will be = 37 %


Case 2 :
In the case of the presence of laminae shale , in this case shale will replace the whole reservoir ( 100 & ) and also will bring its own 10% porosity.
In other words , the porosity will be reduced from 30% to 10%
Case 3 :
In the case of the presence of dispersed shale , in this case shale we will replace the porosity  volume it self ( 30 % ) and as usual it will bring its own porosity.
 
In other words , the porosity will be reduced into 3% ( 30 / 10 )Summarized figure for the different shale distributions in shaly sand reservoir and it’s effect on the reservoir porosity.
Shale distribution model proposed by Thomas and Stieber (Tyagi et al. 2009). Here Vshale is the volume of shale, φtotal is the total porosity, φmax is the maximum porosity, and φsh is the porosity in shale

Conclusion :


 So, we can differentiate between the three different types of shale distribution and according to the type we can make the right interpretation for the porosity and the saturation of the sand reservoir , also we will avoid the miss leading interpretation in the shortcut in the resistivity log.


Photo Credits: Ahmed Adel
Originally blog is written by Ahmed Adel 










Siccar Point - the world's most important geological site and the birthplace of modern geology


Siccar Point is world-famous as the most important unconformity described by James Hutton (1726-1797) in support of his world-changing ideas on the origin and age of the Earth.

James Hutton unconformity with annotations - Siccar Point 



In 1788, James Hutton first discovered Siccar Point, and understood its significance. It is by far the most spectacular of several unconformities that he discovered in Scotland, and very important in helping Hutton to explain his ideas about the processes of the Earth.At Siccar Point, gently sloping strata of 370-million-year-old Famennian Late Devonian Old Red Sandstone and a basal layer of conglomerate overlie near vertical layers of 435-million-year-old lower Silurian Llandovery Epoch greywacke, with an interval of around 65 million years.
Standing on the angular unconformity at Siccar Point (click to enlarge). Photo: Chris Rowan, 2009
As above, with annotations. Photo: Chris Rowan, 2009





Hutton used Siccar Point to demonstrate the cycle of deposition, folding, erosion and further deposition that the unconformity represents. He understood the implication of unconformities in the evidence that they provided for the enormity of geological time and the antiquity of planet Earth, in contrast to the biblical teaching of the creation of the Earth. 

   
How the unconformity at Siccar Point formed.



At this range, it is easy to spot that the contact between the two units is sharp, but it is not completely flat. Furthermore, the lowest part of the overlying Old Red Sandstone contains fragments of rock that are considerably larger than sand; some are at least as large as your fist, and many of the fragments in this basal conglomerate are bits of the underlying Silurian greywacke. These are all signs that the greywackes were exposed at the surface, being eroded, for a considerable period of time before the Old Red Sandstone was laid down on top of them.
The irregular topography and basal conglomerate show that this is an erosional contact. Photo: Chris Rowan, 2009

The Siccar Point which is a rocky promontory in the county of Berwickshire on the east coast of Scotland.