Special Weapon Materials

With the exception of Adamantine armor and weapons, and Mithral armor, fifth edition does not (yet) have any official rules for weapons and armor made from other non-standard materials. If your campaign includes primitive lands, you might need rules for stone or bone. Here are some house rules you may want to use.

The metal weapons and armor in the PHB are assumed to be steel. In primitive areas, steel may not be available. In other areas more advanced materials such as Adamantine or Mithral might be available. Some of these materials grant the item the fragile property – a property that can be applied to both weapons and armor.

The Fragile Property

Fragile Weapons
Fragile weapons cannot take the beating that sturdier weapons can. If you roll a natural 1 on an attack roll with a fragile weapon, you must then make a DC(10) Dexterity (Sleight of Hand) save or that weapon is damaged and only does half damage after that. If already damaged, the weapon is destroyed instead.
Fragile Armor
Armor with the fragile property falls apart when hit with heavy blows. If you are wearing fragile armor and are hit with a critical hit, you must make a DC(10) Dexterity (Acrobatics) save or the armor is damaged and the AC bonus it provides is halved. If already damaged, the armor is destroyed instead.

Adamantine

This is one of the hardest substances in existance.
Adamantine armor
Can be any Medium or heavy armor, but not hide. While you’re wearing it, any critical hit against you becomes a normal hit.
Adamantine weapons
Melee weapons and ammunition made of or coated with adamantine are unusually effective when used to break objects. Whenever an adamantine weapon or piece of ammunition hits an object, the hit is a critical hit.
Cost
The adamantine version of a suit of armor, or a melee weapon or of ten pieces of ammunition costs 500 gp more than the normal version, whether the weapon or ammunition is made of the metal or coated with it.

Mithral

Mithral is a light, flexable metal.
Mithral armor
Can be any Medium or Heavy armor, but not hide. A mithral chain shirt or brestplate can be worn under normal cloths. If the armor normally imposes disadvantage on Dexterity (Stealth) checks or has a Strength requirement, the mithral version of the armor doesn’t.
Mithral weapons
An item made from mithral weighs half as much as the same item made from other metals. Mithral is too light to be used for Heavy weapons. If the weapon isn’t Heavy, it becomes Light. If it is already listed as Light it gains the Finesse property. If the weapon is Two-Handed it is now instead Versatile. Mithral ammunition it too light to be effective.
Cost
The mithral version of a suit of armor or a melee weapon costs 200 gp more than the normal version.

Cold Iron

This iron, mined deep underground, known for its effectiveness against fey creatures, is forged at a lower temperature to preserve its delicate properties. Items made of cold iron weighs one and one half times as much as the same item made from steel.
Cold Iron armor
Can be any Medium or Heavy armor, but not hide. Medium armor imposes a -1 penalty to the DEX modifier for calculating the Armor Class (AC). Heavy armor requires a Str score 2 points higher than that listed in the PHB. Cold iron armor grants a +2 bonus to armor class against any attacks from fey creatures.
Cold Iron weapons
Items without metal parts cannot be made from cold iron. An arrow could be made of cold iron, but a standard quarterstaff could not. Cold iron weapons lose all Light and Finesse properties.  A cold iron weapon grants a +2 bonus to hit against fey creatures. If the creature wielding it has a strength score of 15 or higher,  and the weapon does bludgeoning damage, a +1 bonus is added to damage rolls.
Cost
The cold iron version of a suit of armor or a melee weapon costs twice as much as the normal version.

Steel

Steel is the default metal used for weapons and armor.
Steel is iron ore with unwanted impurities removed and other impurities introduced. These impurities strengthen iron, making it far more resilient.

Iron

Items made of iron weighs one and one half times as much as the same item made from steel.
Iron armor
Can be any Medium or Heavy armor, but not hide. Medium armor imposes a -1 penalty to the DEX modifier for calculating the Armor Class (AC). Heavy armor requires a Str score 2 points higher than that listed in the PHB.
Iron weapons
Items without metal parts cannot be made from iron. An arrow could be made of iron, but a standard quarterstaff could not. Iron weapons lose all Light and Finesse properties.
Cost
Armor and Weapons made from Iron cost the same as those made from steel.

Bronze

Before the advent of iron and steel, bronze ruled the world. This metal can be used in place of steel for both weapons and armor. Bronze is non-ferrous so it doesn’t rust and it is not corroded by Rust Monsters.
Bronze Armor
Bronze can be used to create any medium or light armor made entirely of metal or that has metal components. It protects a creature as well as steel armor does. Bronze armor has the same weight as normal steel armor of its type.
Bronze Weapons
Bronze weapons are cast, not forged so the larger ones (great sword and longsword) may be rare in your campaign. Bronze weapons have the same weight as steel weapons of the same type. Whenever a bronze weapon or piece of ammunition hits an object, the hit only does half damage.
Cost
Armor and Weapons made from bronze cost the same as those made from steel.

Copper

Copper was the first metal to be used for tools, weapons and armor. This easily worked metal can be used in place of steel for both weapons and armor. However, compared to the above metals, it is much softer and requires daily maintenance. Copper is non-ferrous so it doesn’t rust and it is not corroded by Rust Monsters.
Copper Armor
Coper can be used to create any medium or light armor made entirely of metal or that has metal components. It protects a creature as well as steel armor does, but it has the fragile property. Copper armor has the same weight as normal steel armor of its type.
Copper Weapons
Items without metal parts cannot be made from copper. Arrows and weapons with the reach property can be made of wood with only the tips made of copper. Copper weapons have the same weight and do the same damage as steel weapons of the same type but also have the fragile property.
Cost
Armor and Weapons made from copper cost half as much as those made from steel.

Stone

Stone Age weapons almost always utilize stone in some way. From rocks lashed to wooden hafts to create early maces and axes, to flint knives and stone arrowheads, these primitive weapons are still deadly.
Stone Armor
Armor cannot usually be constructed from stone, but advanced, often alchemically enhanced stone armor made by dwarves or other stone-working cultures does exist. They are one third the weight of their base armor, and have the fragile property.
Stone Weapons
Light and one-handed bludgeoning weapons, spears, axes, daggers, and arrowheads can all be made of stone. Weapons made of stone are one third the weight of their base weapons, and have the fragile property.
Cost
Alchemically enhanced stone armor cost twice its standard cost. Weapons made from stone cost one quarter as much as those made from steel.

Bone

Bone can be used in place of wood and steel in weapons and armor. Other animal-based materials like horn, shell, and ivory also use the rules for bone weapon and armor.
Bone Armor
Studded leather, scale mail, breastplates, and wooden shields can all be constructed using bone. Bone either replaces the metal components of the armor, or in the case of wooden shields, large pieces of bone or shell replace the wood. They are one quarter the weight of their base armor, and have the fragile property. The armor/shield bonus of bone armor is reduced by 1. If the armor normally imposes disadvantage on Dexterity (Stealth) checks or has a Strength requirement, the bone version of the armor doesn’t.
Bone Weapons
Light and one-handed melee weapons, as well as two-handed weapons that deal bludgeoning damage only, can be crafted from bone. Hafted two-handed weapons such as spears can be crafted with bone tips, as can arrowheads. Other two-handed weapons cannot be constructed of bone. Bone weapons have the the fragile property. Bone weapons take a –1 penalty on damage rolls (minimum 1 damage).
Cost
Armor and Weapons made from bone cost one tenth as much as those made from steel, but they are not normally available except in those cultures that use them.

Rustic Wood

We are talking here about non-tempered wood that is fashioned by hand with primitive tools into armor or weapons.
Rustic Wood Armor
Studded leather, scale mail, breastplates, and shields can all be constructed using roughly worked wood. Wood replaces the metal components of the armor. They are one quarter the weight of their base armor, and have the fragile property. The armor bonus of rustic wood armor is half that listed in the PHB, except no AC reduction for rustic wood shields. If the armor normally imposes disadvantage on Dexterity (Stealth) checks or has a Strength requirement, the wood version of the armor doesn’t.
Rustic Wooden Weapons
Light and one-handed melee weapons, as well as two-handed weapons that deal bludgeoning damage only, can be crafted from roughly worked wood. Hafted two-handed weapons such as spears can be crafted entirely of wood, as can arrows. Other two-handed weapons cannot be constructed of wood. Rustic Wood weapons have the the fragile property. Rustic Wood weapons take a –2 penalty on damage rolls (minimum 1 point damage).
Cost
Rustic Wood Armor and Weapons are not normally available except in those cultures that use them. A PC might make them himself, or barter for them.