Gemini is the sign associated with communication, intelligence and mimicry. Gemini is ruled by analytical and talkative Mercury. And that is why action oriented Mars feels uncomfortable in Gemini. Gemini maybe a bad placement for Mars but aspects may somewhat cover for this as Mars from Gemini aspects practical Virgo, research oriented Sagittarius and workaholic Capricorn Sign.
The nakshatras associated with Gemini are Mrigashira, Ardra and Punarvasu. Mrigishira is owned by Mars himself while Ardra is owned by Rahu and associated with fierce diety Rudra. So Mars in these nakshatras can turn individual argumentative and confontrational. Punarvasu being owned by Jupiter is perhaps where Mars may receive guidance to stay calm and non confontrational.
Positives: Gemini loves to argue while Mars loves confontration. Most individuals in today's fast paced lives ignore evils in society or individuals who pose problems to others around. Mars in Gemini would confront such evils and individuals and argue for change. Mars in Gemini may appear argumentative to others but Mars seeks to resolve issues rather than ignore them. Mars in Gemini can give excellent debating skills and allow quick verbal retort.
Negatives: Endless arguing and verbal rhetoric often creates problems in family life. Mars in Gemini lacks the grace to admit defeat or accept fault when wrong. Mars in Gemini sometimes creates an over thinker who over analyzes and fails to act when situation demands.
Service Roles: Gemini is quirky and intelligent sign. Combined with action oriented approach and tireless worth ethics of Mars it can make an individual a great asset at workplace especially if work doesn't involve physical labour. Mars in Gemini can produce a very good lawyer and social justice warrior who fight against evils plaguing the society. Mars in Gemini gives excellent debating skills which are ideal for career as a television panelist, in journalism, contract negotiation, court cases and conflict resolution. Mars in Gemini also allow individual to excel as writer, coder/programmer and also in filing litigation cases.
Business: Mars in Gemini can allow starting a law firm, a news media corporation, daily newspaper editorial, printing press which publishes sensationalist and controversial books or perhaps start an NGO which fights for social justice and human rights.
Mars in Gemini is less ideal for marriage life especially if it influences marriage house via placement or aspect. Marriage can have its share of arguments, bickering and misunderstandings. Either individual or his/her spouse can be argumentative and loves finding faults in everything the other spouse does. Mars placed in Mrigishira or Ardra nakshatra and influencing marriage house can cause irrepairable damage via arguments and perhaps even lead to divorce. A little maturity and a lot of forgiving will be required in order to make the marriage life work when Mars is placed in Gemini.
Mars in Gemini can be tough for any relationship where it casts an influence especially for houses where Gemini and Virgo are placed. Relationships associated with houses where Sagittarius and Capricorn are placed may not be that bad. For example: Mars in Gemini placed in second house can cause problems in relationship with family members and children but relationship with in-laws and gurus/mentors may not be that bad inspite of differences.
Social reformer, excellent debating skills and fearless critic.
Argumentative, over thinker, doesn't walk the talk.