23) Which of the following best characterizes ferromagnesian silicates? A) They are black to dark-green, silicate minerals containing iron and magnesium. B) They are mostly clear, colorless, and rich in the elements magnesium and ferrium. C) They contain magnetite and ferroite and they are clear to light green. D) They contain iron and magnetite, are black in color, and they have metallic lusters. 24) Which one of the following describes a mineral’s response to mechanical impact? A) cleavage B) streak C) luster D) crystal form 25) All silicate minerals contain which two elements? A) silicon, oxygen B) iron, silicon C) silicon, sodium D) oxygen, carbon 26) In which type of chemical bonding are electrons shared between adjacent atoms? A) covalent C) subatomic B) isotopic D) ionic
The Correct Answer and Explanation is :
Here are the correct answers to the questions, along with detailed explanations:
23) Which of the following best characterizes ferromagnesian silicates?
Correct Answer: A) They are black to dark-green, silicate minerals containing iron and magnesium.
Explanation: Ferromagnesian silicates, also known as mafic minerals, are silicate minerals rich in iron (Fe) and magnesium (Mg). The term “ferromagnesian” combines “ferro,” referring to iron, and “magnesian,” referring to magnesium. These minerals typically exhibit dark colors, ranging from black to dark green, due to their iron and magnesium content. Common examples include olivine, pyroxene, amphibole, and biotite. Their dark coloration and higher density distinguish them from non-ferromagnesian (felsic) silicates, which are lighter in color and density.
24) Which one of the following describes a mineral’s response to mechanical impact?
Correct Answer: A) Cleavage
Explanation: Cleavage refers to a mineral’s tendency to break along specific planes of weakness within its crystal structure. These planes are determined by the arrangement and bonding of atoms in the mineral. When mechanical force is applied, minerals with good cleavage will split smoothly along these planes, resulting in flat, even surfaces. This property is a key diagnostic feature in mineral identification. In contrast, minerals without cleavage may fracture irregularly. Other properties mentioned, such as streak (the color of a mineral’s powder), luster (the way a mineral reflects light), and crystal form (the external shape of a crystal), do not describe a mineral’s response to mechanical impact.
25) All silicate minerals contain which two elements?
Correct Answer: A) Silicon, oxygen
Explanation: Silicate minerals are characterized by the presence of silicon (Si) and oxygen (O) atoms arranged in a tetrahedral structure, where one silicon atom is bonded to four oxygen atoms. This fundamental building block, known as the silica tetrahedron, can link together in various ways to form different silicate structures, such as chains, sheets, or frameworks. The diversity in silicate minerals arises from the various ways these tetrahedra combine and the incorporation of other elements, but all silicate minerals share the common feature of containing silicon and oxygen.
26) In which type of chemical bonding are electrons shared between adjacent atoms?
Correct Answer: A) Covalent
Explanation: Covalent bonding involves the sharing of electrons between adjacent atoms to achieve stability in their electron configurations. This type of bond is typically strong and results in minerals with high hardness and melting points. For example, in a silicon-oxygen tetrahedron, each silicon atom shares electrons with four oxygen atoms, forming strong covalent bonds. In contrast, ionic bonding involves the transfer of electrons from one atom to another, resulting in positively and negatively charged ions that attract each other. Metallic bonding, another type, features a ‘sea’ of delocalized electrons shared among a lattice of metal atoms, allowing for properties like electrical conductivity.
Understanding these fundamental concepts is essential in geology and mineralogy, as they explain the physical and chemical properties of minerals, influencing their identification, classification, and practical applications.