Brooch is part of equipment given upon reaching level 65 and can be upgraded to higher gear. Basic Parthian Brooch has one optional rollable line. Higher tier brooches have two rollable enigmatic lines. Most classes choose 3 power, 6 crit factor.
Parthian Brooches come in two varieties. Fancy one gives 2 crit factor and Ferocious 1 power. It you got wrong one for your class, brooch can also be bought from Vanguard Initiative merchant for 3 credits. Parthian Brooch should be upgraded asap as you gather 6 Silver Talents and 25 Metal Fragments. Upgrade has 100% chance to succeed.
Fancy Parthian Brooch upgrades to Simple Quickcarve Brooch and Ferocious to Simple Empowered Brooch. These are brooches can be activated every 3 minutes to give 15 seconds crit rate+attack speed buff or power buff. Drag brooch to shortcut tray and use that shortcut to activate it. Brooch should always be combined with class specific boost skills and rather boss enrage for maximum effect. This equipment gathers item XP to improve upgrade chances.
Simple Quickcarve Brooch/Simple Empowered Brooch can be upgraded to superior Quickcarve Brooch/Empowered Brooch, which are similar but have bit higher stats.
Quickcarve Brooch/Empowered Brooch can be upgraded to Quatrefoil Brooch.
Quatrefoil combines power, crit factor and attack speed buff and in addition removes harmful effects from character. Latter means it works like priest casting Cleanse and removes ie. HP drain debuffs or stuns. Cleanse is especially important for tanks and healers and for PVP.
Unfortunately getting Quatrefoil is extremely expensive. Upgrade costs 2 Diamonds among other materials and has 10% base chance to succeed (doubled with item XP).
As of Exodor patch success chance was raised to 25% and attempt only costs 9 Emeralds.
There has occasionally been event dungeons that drops items which make upgrading to Quatrefoil more easy.
In later patches Quatrefoil can be upgraded to Powerful Goddess's Brooch and Marrow Brooch to Dracoloth Brooch. These have only minor increase in stats and effect is same. Visuals however are different.
Brooches have been in TERA for a long time. First ones where released during level cap 60 times. Before gear rework brooches were dungeons drops and superior versions had to be crafted. One might rarely find crafted superior brooch on Trade Broker, where Quatrefoil costs ~750 000 gold.
Level 60 Flawless Brooch Boxes dropped in easy gearing/farming dungeons and Flawless Brooches are tradeable. One can still probably find level 60 brooch from Trade Broker for level 60-65 questing.
Marrow Brooch has similar effect to Quatrefoil Brooch, but it last 20 seconds. This type is only available from Harrowhold after obtaining Vergos's Head. Marrow Brooch is not available anymore as Harrowhold was removed in patch 79.
Note: Marrow Brooch is banned from some battlegrounds, like Shore Hold.
There existed Sturdy Parthian Brooch, Simple Grounding Brooch and Grounding Brooch. These were meant for tanks and had "Attacks draw 3/6/12% more aggro" lines. Active effect was increasing Endurance for 15 seconds. These were rarely used even by tanks and this type is not available anymore.
There's also Simple Cleansing Brooch/Cleansing Brooch that has cleansing effect (6 min/3 min cooldown) like Quatrefoil had. These were meant for cheaply gearing your healer or other class which needed cleaning effect ie. for removing stuns. These were purely dungeon drops and can't currently be acquired.
There has occasionally been event dungeons that drop Cleansing Brooches, which makes gearing healers cheaper.